189 
,S7 
I Copy 1 



EXPERIMENTS IN FIELD PLOT 

TECHNIC FOR THE PRELIMINARY 

DETERMINATION OF COMPARATIVE 

YIELDS IN THE SMALL GRAINS 



BY 



Lewis John Stadler, B. S. A., A. M. 



Submitted in Partial Fulfillment of the 

Requirements for the Degree of 

Doctor of Philosophy 



IN THE 

GRADUATE SCHOOL 



OF THE 



UNIVERSITY OF MISSOURI 
COLUMBIA, MISSOURL 
192L 



EXPERIMENTS IN FIELD PLOT 

TECHNIC FOR THE PRELIMINARY 

DETERMINATION OF COMPARATIVE 

YIELDS IN THE SMALL GRAINS 



BY 



Lewis John Stabler, B. S. A., A. M. 



Submitted in Partial Fulfillment of the 

Requirements for the Degree of 

Doctor of Philosophy 



IN THE 

GRADUATE SCHOOL 

OF THE 

UNIVERSITY OF MISSOURI 

COLUMBIA, MISSOURI. 

1921. 



UNIVERSITY OF MISSOURI S"^ 

COLLEGE OF AGRICULTURE 

Agricultural Experiment Station 



BOARD OF CONTROL, 

THE CURATORS OF THE UNIVERSITY OF MISSOURI 



E. LANSING RAY, 

St. Eouis 



EXECUTIVE BOARD OF THE UNIVERSITY 
P. E. BURTON, 
Joplin 



H. J. BLANTON, 
Paris 



ADVISORY COUNCIL 

THE MISSOURI STATE BOARD OF AGRICULTURE 



OFFICERS OF THE STATION 

F. B. MUMFORD, M. S., DIRECTOR 
J. C. JONES, Ph. D., LL.D., PRESIDENT OF THE UNIVERSITY 



STATION STAFF 

DECEMBER, 1921 



AGRICULTURAL CHEMISTRY 

C. R. MouLTON, Ph. D. 
L. D. Haigh, Ph. D. 
W. S. Ritchie, A. M. 
E. E. Vanatta, M. S. 

A. R. Hall, B. S. in Agr. 

E. G. SiEvEKiNG, B. S. in Agr. 

AGRICULTURAL ENGINEERING 
J. C. WOOLEY, B .S. 
Mack M. Jones, B. S. 

ANIMAL HUSBANDRY 

E. A. Trowbridge, B. S. in Agr. 
L. A. Weaver, B. S. in Agr. 

A. G. HoGAN, Ph. D. 

F. B. MuMFORD, M. S. 

D. W. Chittenden, B. S. in Agr. 
A. T. Edinger, B. S. in Agr. 

H. D. Fox, B. S. in Agr. 

BOTANY 
W. J. Robbins, Ph. D. 

E. F. Hopkins, Ph. D. 

DAIRY HUSBANDRY 

A. C. RagsdalE. B. S. in J^gr. 
W. W. Swett, A. M. 

Wm. H. E. Reid, a. M. 
Samuel Brody, M. A. 

C. W. Turner, B. S. in Agr. 

D. H. Nelson, B. S. in Agr. 

ENTOMOLOGY 
Leonard Haseman, Ph. D. 
K. C. Sullivan, A. M. 
O. C. McBride, 

FIELD CROPS 
W. C. Etheridge, Ph. D. 
C. A. Helm, A. M. 
L. J. Stadler, a. M. 
O. W. Letson, B. S. in Agr. 

B. M. King, B. S. in Agr. 
A. C. Hill, B. S. in Agr. 
Miss Bertha C. Hite, A. B.> 
Miss Pearl Drummond, A. A.* 



RURAL LIFE 



O. R. Johnson, A. M. 
S. D. Gromer, a. M. 

E. L- Morgan, A. M. 

Ben H. Frame, B. S. in Agr. 

HORTICULTURE 

V. R. Gardner, M. S. A. 
H. D. Hooker, Jr., Ph. D. 
J. T. Rosa, Jr., M. S. 

F. C. Bradford, M. S. 

H. G. Swartwout, B. S. in Agr. 

POULTRY HUSBANDRY 

H. L. Kempster, B. S. 
Earl W. Henderson 

SOILS 

M. F. Miller, M. S. A. 
H. H. Krusekopf, a. M. 
W. A. Albrecht, Ph. D. 
F. L. DuLEY, A. M.^* 
R. R. Hudelson, a. M. 
Wm. DeYoung, B. S. in Agr. 
H. V. Jordan, B. S. in Agr. 
Richard Bradfield, A. B. 
O. B. Price, B. S. in Agr. 

VETERINARY SCIENCE 

J. W. CONNAWAY, D. V. S., M. D. 

L. S. Backus, D. V. M. 
O. S. Crisler, D. V. M. 
A. J. DuRANT, A. M. 
H. G. Newman, A. M. 

OTHER OFFICERS 

R. B. Price, M. S., Treasurer 

Leslie Cowan, B. S., Sercretary 

S. B. Shirkey, a. M., Asst. to Director 

A. A. Jeffrey, A. B., Agricultural Editor 

J. F. Barham, Photographer 

Miss Jane Frodsham, Librarian 

E. E. Brown, Business Manager 



Hn service of U. S. Department of Agriculture, Seed Testing Laboratory. 
^On leave of absence. ». ._^...,— ' , ■:■ 

\ LIBf^Afr^.OF CONGRE39 






CONTENTS 

Page 

The Problem 6 

Plan and Method of Investigation 9 

Terminology 9 

Procedure 11 

Work of 1919 12 

Work of 1920 16 

Work of 1921 18 

Competition as a Source of Error in Preliminary Tests 23 

Previous Investigation 23 

Experimental Results 25 

Illustrations of Eflfects of Competition 26 

Relation of Competition to Various Characteristics of the Com- 
peting Varieties 31 

Discussion 40 

Size and Replication of Plots 43 

Previous Investigation 43 

Experimental Results 44 

Size of Plots 44 

RepHcation of Plots 50 

Adjustment of Yields by Means of Check Plots 54 

Previous Investigation 54 

Experimental Results 56 

Method Used in Adjusting Yields 58 

Relative Variability of Actual and Adjusted Yields 60 

Difference in Results Obtained by Adjustment with Different Check 

Varieties 63 

Value and Limitations of Adjusting Yields by Means of Check Plots 71 

Concluding Remarks 12) 

Summary 75 

Acknowledgment 11 

References Cited 78 



TABLES 

Table 

Number Table Page 

1 Yields of Barley Varieties 1919 13 

2 Yields of Oats Varieties 1919 14 

3 Yields of Oats Strains 1919 15 

4 Yields of Wheat Varieties 1920 16 

5 Yields of Wheat Varieties 1921 17 

6 Yields of Wheat Varieties and Mixtures 1921 18 

7 Yields of Oats Varieties 1921 21 

8 Yields of Oats Strains 1921 22 

9 Relative Yields of Two Small Grain Varieties When Compared in Al- 

ternate Rows and in Blocks (Kiesselbach) 24 

10 Correlation of Competition with Various Characteristics in Barley Va- 

riety Test 1919 35 

11 Correlation of Competition with Various Characteristics in Oats Va- 

riety Test 1919 35 



4 Tables 

12 Correlation of Competition with Various Characteristics in Oats Strain 

Test 1919 36 

13 Correlation of Competition with Various Characteristics in Wheat Va- 

riety Test 1920 n 

14. Correlation of Competition with Various Characteristics in Wheat Va- 
riety Test 1921 Z1 

15 Correlation of Competition with Various Characteristics in Wheat Mix- 

ture Test 1921 38 

16 Correlation of Competition with Various Characteristics in Oats Va- 

riety Test 1921 39 

17 Summary of Effects of Competition in All Tests 41 

18 Correlation of Yield with Dates of Heading and Maturity in Variety 

Tests of Barley, Oats, and Wheat 42 

19 Yield and Variability of 1-row, 3-row, and 5-row Check Plots in Bar- 

ley Variety Test 1919 45 

20 Yield and Variability of 1-row, 3-row, and 5-row Check Plots in Oats 

Variety Test 1919 46 

21 Yield and Variability of 1-row, 3-row, and 5-row Check Plots in Oats 

Strain Test 1919 47 

22 Yield and Variability of 1-row, 3-row, and 5-row Check Plots in Wheat 

Variety Test 1920 47 

23 Yield and Variability of 3-row and 5-row Check Plots in Wheat and 

Oats Test 1921 48 

24 Yield and Variability of 3-row and 5-row Test Plots in All Tests 50 

25 Relation of Plot Variability to Size of Experiment Field in Wheat Va- 

riety Test 1920 51 

26 Relation of Plot Variability to Size of Experiment Field in Wheat Va- 

riety Test 1921 52 

27 Relation of Plot Variability to Size of Experiment Field in Oats Va- 

riety and Strain Tests 1921 52 

28 Soil Heterogeneity of an Experiment Field as Determined from Yields 

of Two Check Varieties 53 

29 Effect on Plot Variability of Adjusting Yields by Check Plots (Kies- 

selbach ) 55 

30 Reduction of Variability by the Use of Check Plots Equivalent to That 

Probably Attainable with the Same Number of Plots by Replication . 57 

31 Relative VariabiHty of Actual and Adjusted Yields in Barley Variety 

Test 1919 59 

32 Relative Variability of Actual and Adjusted Yields in Oats Variety 

Test 1919 60 

i2) Relative Variability of Actual and Adjusted Yields in Oats Strain 

Test 1919 61 

34 Relative Variability of Actual and Adjusted Yields in Wheat Variety 

Test 1920 62 

35 Relative Variability of Actual and Adjusted Yields in Wheat Variety 

Test 1921 64 

36 Relative Variability of Actual and Adjusted Yields in Wheat Mixture 

Test 1921 65 

Zl Relative Variability of Actual and Adjusted Yields in Oats Variety 

Test 1921 66 

38 Relative Variability of Actual and Adjusted Yields in Oats Strain 

Test 1921 67 

39 Relative Variability of Actual and Adjusted Yields of Kherson and Red 

Rustproof Oats Each in 120 Distributed Plots, in Oats Variety and 
Strain Tests 1921 68 

40 Summary of Relative Variability of Actual and Adjusted Yields of 

Interior Rows in All Tests 1921 71 



EXPERIMENTS IN FIELD PLOT TECHNIC 
FOR THE PRELIMINARY DETERMINA- 
TION OF COMPARATIVE YIELDS IN 
THE SMALL GRAINS 

L. J. Stadler 

During recent years the investigation of the reliability of field 
experiments has become an important phase of agronomic research. 
Field experiments as ordinarily conducted have been shown to be 
affected by many gross errors. In the light of these investigations it 
has become apparent that the results of many of the older experiments 
are inconclusive or even misleading. Various expedients have been 
suggested for counteracting experimental error. Some of these have 
been quite successful, while others have probably done more harm 
than good. 

The pioneer investigations in this field have been of great 
value in directing attention to the important sources of error and in 
suggesting possible means for their control. Doubtless at the present 
time most of the major sources of error are recognized. But the true 
extent of the errors and the actual practical value of the methods of 
counteracting them can be determined only by numerous investiga- 
tions of experimental methods under different conditions. 

The present paper is concerned with experimental error and field 
plot technic in preliminary variety and strain tests with the small 
grains. The same type of test is extensively used in small grain im- 
provement, not only in the preliminary testing of varieties, but also 
in the comparison of strains and selections. Although the small plot 
test is particularly subject to errors of certain sorts, it has a decided 
advantage over tests in larger plots in the possibility of extensive 
replication, which is probably the greatest single factor in the reduc- 
tion of experimental error. It should be possible, consequently, to 
obtain extremely accurate results in small plot tests without the use 
of large experimental areas, when the errors peculiar to the small 
plot are understood and controlled. 



(5) 



6 Missouri Agr. Exp. Sta. Research Bulletin 49 

THE PROBLEM. 

At present the type of plot most commonly used for the pre- 
liminary testing of small grain varieties and strains is probably the 
"rod-row." The methods of conducting rod-row tests described by 
Love and Craig' may be considered typical. The varieties or strains 
are sown by hand in rows one foot apart, usually opened and covered 
with a wheel hoe or similar implement. The seed for each row is 
weighed out in a quantity equivalent to ordinary rates of seeding in 
field practice. In harvesting, six inches or a foot at the end of the 
row is discarded, to prevent increase in yield by reason of the more 
favorable space conditions at the ends of the rows. The list of va- 
rieties is repeated in several series, and the results averaged to reduce 
the error from plot variability. A check variety is grown in every 
tenth row to indicate the variability of the field. 

The use of rod-row tests involves several errors, derived principally 
from the modified conditions under which the plants are grown. The 
object of the test is to discover the relative value of the strains under 
field conditions, and therefore any modification of field conditions 
which may favor some sorts more than others introduces error. The 
wide spacing between rows, with consequently heavier seeding in the 
row for any given rate of planting; the hand seeding and covering, re- 
sulting usually in slightly ridged rather than slightly furrowed rows ; 
and the growing of different varieties in single rows, in competition 
with other varieties rather than with their own kind, are examples of 
typical conditions which may be expected to favor some varieties more 
than others. Consequently the best varieties in the rod-row test are 
not necessarily the best varieties under field culture, even when soil and 
seasonal variability are reduced to the minimum by replication of plots 
and repetition of the test through a series of seasons. 

Such sources of error as those mentioned do not necessarily affect 
the variability of the yields of replicate plots, as Kiesselbach' has 
pointed out, and are therefore more likely to escape notice. They are 
systematic errors affecting the yields of replicate plots similarly. 
Marked superiority of Turkey wheat over Fulcaster in a variety test 
in Kansas does not indicate the superiority of Turkey over Fulcaster 
in Illinois, no matter how low plot variability in the variety test may 
be, because the growing conditions in Illinois are different from the 
growing conditions in Kansas. Similarly the superiority of Turkey 
wheat over Fulcaster in a rod-row test may not mean its superiority 
under field conditions in the same locality, because here again growing 



Experiments in Field Plot Technic 7 

conditions are different. The error in applying the results, though of 
course much less in degree, is similar in kind. And, since the rod-row 
test has no purpose but to indicate the relative value of the strains 
tested, for field conditions, any pronounced tendency to favor some 
varieties at the expense of others is fatal to its object. 

Ordinarily, however, the rod-row test is only the first stage in 
variety testing, and final recommendations are based upon results of 
tests under conditions which approach those of field culture more 
closely. When the elimination of varieties in the rod-row tests is 
not extremely strict a considerable latitude may be allowed, and under 
these conditions the rod-row test has served a valuable purpose. It 
is of course desirable nevertheless to reduce these errors to the greatest 
possible extent. 

Probably the most important of the errors mentioned is that arising 
from the competition between different varieties, in the single-row test. 
Obviously a variety grown in a single row between two different va- 
rieties may yield considerably more or less than the same variety 
grown between two rows of its own kind. Various expedients for re- 
ducing varietal competition have been suggested. Sometimes the order 
of varieties is changed in each series to bring together different va- 
rieties and thus tend to equalize the effects of competition; sometimes 
an attempt is made to grow the varieties in such order as to bring 
together those of similar habit, and thus to reduce the effects of 
competition. Probably the most effective method is to grow border 
rows which may be discarded, and some investigators therefore use 
three-row or five-row blocks, in which the outer row on each side is 
discarded. 

The principal objection to the use of border rows in the increased 
area required to test the same number of strains, and the large pro- 
portion of the crop which is not harvested for yield. This is par- 
ticularly true when 3-row blocks are used, since in this case two- 
thirds of the field is used for border protection. The border rows may 
be us,ed for seed, but two-thirds of the field is of course much more 
than is required ordinarily for this purpose. When 5-row blocks are 
used the proportion of the crop harvested for yield is increased from 
one-third to three-fifths, though it is an increase in size of plot, with 
some decrease in replication, so that there may be no gain in accuracy. 
There is a possibility that the effect of competition on the yield of 5-row 
blocks may be slight enough to permit the harvesting of all five rows 
for yield, particularly if the varieties may be effectively arranged for 
the reduction of competition. At any rate, in such plots the error 
from competition may be expected to be much less than that in single- 



8 Missouri Agr. Exp. Sta. Research Bulletin 49 

row plots, since only two of the five rows are subject to competition 
with a different variety, and each of these is subject to such compe- 
tition on only one instead of on both sides. 

Another phase of the question which should not be overlooked 
is the effect of adding border rows on the error from soil variability. 
If, for example, each rod-row is to be protected from competition by 
two border rows, the test will require three times as large a field as 
the same test without the border rows. This can hardly fail to in- 
crease materially the variability of the yields of replicate plots, to an 
extent which will vary with the uniformity of the field concerned. 
The use of border rows may thus necessitate the use of an even greater 
number of replications for the same degree of accuracy, as far as 
plot variability is concerned. It is possible that 3-row plots (whether 
or not provided with border rows) may require less replications 
for a given degree of accuracy than single-row plots, on account of 
their larger size. It is possible also that 5-row plots, because of 
their size, may have an advantage over 3-row plots in reducing va- 
riability, great enough to justify in practice harvesting all five rows 
for yield, rather than harvesting the interior three rows and discarding 
the border rows. 

The importance of any practice that will reduce the variability of 
the replicate plots is thus increased when border rows are introduced. 
A familiar method for this purpose is the adjustment of yields by 
means of distributed check plots. In following this method the yields 
of check plots are considered measures of the productivity of the 
soil, which is usually assumed to vary uniformly between them. The 
yields of the experimental plots are adjusted on the basis of uniform 
productivity of the field as a whole. Of late this method has rather 
lost favor among agronomists. In some cases the adjustment actually 
increases rather than decreases the variability of the replicate ex- 
perimental plots. Check plots have not been used extensively in ad- 
justing yields in rod-row tests, principally because of the great in- 
crease in computation necessary in adjusting the yields of such a large 
number of plots. 



Experiments in Field Plot Technic 9 

PLAN AND METHOD OF INVESTIGATION 

The experiments here reported were designed to obtain informa- 
tion on several factors affecting the accuracy of preHminary variety 
and strain tests, with a view to devising, if possible, an improved 
technic for this important phase of crop improvement work. The 
data obtained bear directly on the following points: 

1. The extent of error from varietal competition in bor- 
der rows, and the relation of such competition to the charac- 
teristics of the varieties, 

2. The relative variability of plots of 1, 3, and 5 rows, and 
the number of replications necessary for a given degree of 
precision with plots of the three sizes, and 

3. The effect on variability of adjusting yields by means 
of check plots. 

Terminology. — In this report the term plot will be used to des- 
ignate an area on which a single variety or strain is grown, in com- 
parison with other varieties or strains, m other plots. The plot may 
consist of one or more rows. A plot of more than one row may also be 
referred to as a block. The single outside rows of the block are the 
border rows. A single-row plot protected from competition by border 
rows, which are to be discarded, will be spoken of as a protected 
single-row plot. A protected single-row plot is therefore a 3-row plot 
with border rows discarded, and a protected 3-row plot is a 5-row plot 
with border rows discarded. The phrase "3-row plots replicated five 
times" will be used to refer to 3-row plots in five systematically dis- 
tributed locations, not in six. The area on which a complete variety 
or strain test is conducted is spoken of as an experiment field, or simply 
a field. A group of plots including one plot of each variety or strain 
tested is a series. When four replications are used there are four 
series of plots. The group of contiguous plots from one side of the 
field to the other constitutes a range. The ranges are separated by 
alleys. 

Thus the field shown in figure 1 consists of sixteen ranges, each 
range including twenty-nine 5-row (or protected 3-row) plots. Ninety- 
six varieties were tested on this field, each replicated four times. 
Ranges I to IV, inclusive, make up the first series, V to VIII the sec- 
ond, IX to XII the third, and XIII to XVI the fourth. Each of the 
four strips running lengthwise of the field and separated by the check 
plots may also be considered a series. 

All yields are expressed in bushels per acre by weight, computed 
on the basis of 60 pounds per bushel for wheat, 48 pounds for barley, 



10 



Missouri Agr. Exp. Sta. Research Bulletin 49 



B 



CH 



n 



33 



id 



65 



81 



CH 



21 



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Figure 1.— Planting Plan of Wheat Variety Tests 1920 and 1921. 
Legend: B, border. CK, check. Numbers 1-96, planting numbers of varieties 
tested as given in Tables 4 and 5. 



Experime;nts in Field Plot Technic 11 

and 32 pounds for oats. The measures of variability used are the 
average deviation, the standard deviation, and the probable error. 
These were computed according to the following formulae : 




in which A.D. = average deviation, o-==standard deviation, E = prob- 
able error (of a single determination), d == the deviation of a single 
variate from the mean, and n = the number of variates. The correla- 
tion coefficient r was determined by the formula 

\ n / \o-xo-y 

and the probable error of the correlation coefficient Er by the formula 

.6745 (1 — r^) 



E,= ±- 



Vn 



The tests reported are of two kinds, variety tests and strain tests. 
The variety tests were comparisons of commercial varieties, most 
of which were taxonomically distinct. A number of pure line selec- 
tions were included in the wheat variety tests. The strain tests were 
comparisons of a considerable number of commercial lots of the same 
variety obtained from different sources. These strains, so-called for 
convenience, are not, except in a very few cases, pure lines. Some of 
them are possibly identical, and all the strains of any one variety are 
of course very similar, since they are taxonomically the same. 

Procedure.— In the seasons of 1919, 1920, 1921, tests of va- 
rieties and strains of oats, barley, and wheat were conducted in blocks 
consisting of five rows ten inches apart and usually 18 feet long. 
From 24 to 96 varieties were included in each test, and from three to 
six (usually four) replications were used. The planting order in each 
case was designed on a plan similar to that illustrated in figure 1. 
It will be noted that the check plots were in continuous strips, that 
each variety was represented in each quarter of the field, whether 
divided from east to west or from north to south, and that in all 
four series each variety occupied the same position with relation to 
the check plots, and had the same varieties adjoining it on either side. 



12 



Missouri Agr. Exp. Sta. Research Bulletin 49 



The rows in some cases ran east and west, and in some cases north 
and south. 

All these plots were seeded with a 5-row nursery drill, built from 
plans furnished by Professor T. A. Kiesselbach of the Nebraska Sta- 
tion. This is a hoe drill designed for rapid and thorough cleaning 
between plots. Photographs of it have been published in reports of 
earlier work on field plot technic at the Nebraska Station (Mont- 
gomery" page 57, and Kiesselbach " page 16). Its use resulted in uni- 
form seeding and covering and accurate spacing between rows, with a 
close approach to ordinary field conditions in the state in which the 
field was left after seeding. Each field was seeded in a single day. 

All plots were harvested by hand with sickles, a foot at each 
end of each row discarded, and the remainder (usually 16 feet) tied 
in a bundle and hung in a ventilated shed to dry. In 1919 and 1920 
each row was bundled and threshed separately; in 1921 the border 
rows of each 5-row block were bundled separately and the three in- 
terior rows bundled together. Yields were determined by weighing 
in grams at the time of threshing. All final yields were converted 
to bushels per acre and are so expressed. 

Work of 1919. — In 1919 tests were conducted with barley and 
oats. Thirty varieties of barley were grown, each in 3 replicate plots. 
The test comprised three ranges of 185 rows each, including 21 check 
plots, or one in every sixth plot. The barley was drilled at the rate 
of eight pecks per acre, on March 21, in rows running north and south. 
The rows were 14 feet long and 10 inches apart. They were cut to 12 
feet in harvesting. The planting plan is shown in figure 2. Conditions 



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Figure 2. — Planting Plan of Barley Variety Test 1919. Legend: B, 
border. CK, check. Numbers 1-30, planting numbers of varieties tested, as 
given in Table 1. 

were fairly favorable, and the yields of the adapted varieties were 
slightly higher than the average obtained under the conditions at Co- 
lumbia. Two varieties, Italian and Australian White, gave extremely 
low yields and were excluded. Another, Sandrel, was represented 
only in two series, and was also excluded. The yields of the remain- 



Experiments in Field Plot Technic 



13 



ing 27 varieties are shown in Table 1. The planting numbers given in 
this table correspond to those shown in the diagram of the field (figure 
2.) 

Table l. — ^Yields of Barley Varieties. 
In Bushels per Acre. 1919. 



Planting 




Average Yield 


number 


Variety 


3 interior rows 


5 rows 


1 


Hanna 906 


12.55 


12.57 


2 


Steigum 907 


19.90 


19.65 


3 


Luth 908 


23.65 


23.40 


4 


Eagle 913 


20.40 


20.13 


5 


Italian 914* 


6.70 


6.57 


6 


Servian 915 


19.85 


19.86 


7 


Odessa 916 


13.75 


13.41 


8 


Lion 923 


21.75 


22.14 


9 


Australian White 925* 


1.45 


1.74 


10 


Horn 926 


21.25 


21.54 


11 


Odessa 927 


20.80 


19.53 


12 


Summit 929 


23.05 


24.03 


13 


Mariout 932 


18.75 


18.15 


14 


Odessa 934 


10.30 


9.84 


15 


Peruvian 935 


22.25 


20.55 


16 


Trebi 936 


30.90 


30.96 


17 


Sandrel 937* 


35.90 


33.48 


18 


Oderbrucker 940 


23.35 


23.79 


19 


Prankish 953 


22.50 


22.05 


20 


Manchuria 956 


30.80 


30.03 


21 


Oderbrucker 957 


29.45 


29.52 


22 


Manchuria x Champion of Vermont 959 


18.30 


17.49 


23 


Luth 972 


25.05 


26.28 


24 


Red River 973 


27.25 


28.14 


25 


Featherston 1118 


28.25 


27.00 


26 


Featherston 1119 


25.80 


25.83 


27 


Featherston 1120 


34.35 


35.49 


28 


Hanna x Champion of Vermont 1121 


13.75 


13.92 


29 


Manchuria 1125 


20.35 


20.94 


30 


Malting 1129 


17.25 


16.44 




Mean 


22.06 


21.95 



Forty varieties of oats were compared in 1919, but only 24 of 
these could be replicated 4 times and the remaining 16 were duplicated. 
The planting plan was therefore arranged as for 32 varieties, and 
these 16 varieties grown in two plots each in place of eight varieties 



*Italian 914 and Australian White 925 were omitted from all computations because of 
their extremely low yields, and Sandrel 937 because omitted in the third series. 



14 



Missouri Agr. Exp. Sta. Research Bulletin 49 



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Figure 3. — Planting Plan op Oats Variety and Strain Tests 1919. 
Legend: B, border. CK, check. Numbers 1-40 in first four ranges, planting 
numbers of oats varieties, as given in Table 2. Numbers 1-15 in last three 
ranges, planting numbers of oats strains, as given in Table 3. X, test plots 
planted to check variety because of insufficient supply of seed. 

Table 2. — Yields of Oats Varieties. 
In Bushels per Acre. 1919. 



Planting 




Average yield 


in interior rows 


number 


Variety 


Four series 


Three series 


1 


A. Sterilis nigra 


30.0 


31.7 


2 


Black Mesdag 


44.2 


44.7 


3 


C. I. 602 


35.4 


38.1 


4 


C. I. 603 


53.9 


55.1 


5 


C. I. 620 


13.1 


14.1 


6 


Early Champion 


55.5 


53.9 


7 


Early Gothland 


54.1 


52.8 


8 


Carton 473 


30.6 


31.7 


9 


Carton 585 


21.7 


23.0 


10 


Colden Ciant 


42.0 


44.9 


11 


Irish Victor 


69.6 


70.2 


12 


Japan Selection 


47.9 


50.9 


13 


June 


43.1 


44.5 


14 


Kherson Selection 


67.2 


63.1 


15 


Fulghum 042 


60.9 


57.1 


16 


Lincoln 


51.5 


50.3 


17 


Monarch 


56.0 


53.4 


18 


North Finnish 


51.0 


49.5 


19 


Scottish Chief 


59.3 


60.1 


20 


Sparrow bill (Missouri) 


39.8 


41.3 


21 


Sparrow bill (Cornell) 


42.3 


45.7 


22 


Tobolsk 1 


52.6 


57.3 


23 


Tobolsk 2 


46.1 


51.9 


24 


White Tartar 


49.7 


50.3 




Mean 


46.6 


47.3 



EXPEIRIMENTS IN FlELD PlOT TeCHNIC 15 

in four plots each, as shown in figure 3. The rows were 14 feet long 
and were cut to 12 feet in harvesting. This is a convenient size of 
plot for oats tests with 10 inches distance between rows, when the 
border rows are discarded, since the total yield of three rows in 
grams, divided by 10, gives the yield in bushels per acre. The oats 
were planted at the rate of 10 pecks per acre, on March 18, in rows 
running north and south. The season was favorable and a good yield 
of the better varieties was obtained. The yields of the 24 varieties 
replicated four times are shown in Table 2. 

The oats strain test was conducted on the same field, as shown in 
figure 3, directly south of the oats variety test. In planting, these two 
tests were handled as one ; and the rate, date, and method of planting 
were the same. The strains tested were 15 strains of oats obtained 
•under the name Red Rustproof from various experiment stations and 
seedsmen. Three of these strains, 0121, 0124, and 0127, were not true 
to name, but the remainder were taxonomically Red Rustproof oats, 
as described by Etheridge^ The oats strains were tested in six series, 
with check plots in every sixth plot. The line of check plots on the west, 
however, gave abnormally low yields, probably because they were 
located partly on a dead furrow at the edge of the experiment field. 
On account of shortage of seed some of the varieties could not be 
planted in the last series. The first and last series were therefore dis- 

Table 3. — Yields of Oats Strains (Red Rustproof). 
In Bushels per Acre. 1919. 

Planting Accession Average yield 

number number 3 interior Rows 5 Rows 



1 


0119 


2 


0120 


3 


0121* 


4 


0123 


5 


0123 


6 


0125 


7 


0126 


8 


0127* 


9 


0124* 


10 


0133 


11 


0128 


12 


0129 


13 


0130 


14 


0131 


15 


0132 




Mean 



49.58 


49.41 


45.83 


44.51 


49.43 


53.01 


47.85 


49.59 


53.55 


53.47 


50.18 


49.19 


44.85 


45.81 


38.55 


36,67 


63.90 


67.46 


48.00 


46.49 


53.55 


53.15 


49.35 


49.01 


52.73 


51.89 


48.60 


47.84 


55.13 


55.44 


50.07 


50.20 



*Not taxonomically Red Rustproof. 



16 



Missouri Agr. Exp. Sta. Research Bulletin 49 



carded. The average yields of the 15 strains in the four remaining 
series are shown in Table 3. 

Work of 1920. — ^Wheat varieties were grown in 5-row blocks in 
1919-20. Ninety-six varieties were included in the test, four replica- 
tions being used. Fultz wheat was grown as a check in every sixth 
plot. The rows were 18 feet long and were cut to 16 feet in harvest- 
ing. The direction of the rows was east and west. The planting plan 
is shown in figure 1. The wheat was sown October 15, at the rate of 
6 pecks per acre. There was considerable winter injury in the plots 
and the condition of the wheat in early spring was rather poor. The 
yields obtained are shown in Table 4. 



Table 4. — Yields of Wheat Varieties. 
In Bushels per Acre 1920. 



Average yield 
Planting 3 Interior 5 

number Variety Rows Rows 

1 Beechwood Hybrid No. 12.. 10.8 11.1 

2 Beechwood Hybrid No. 81.. 12.8 14.1 

3 Beechwood Hybrid No. 85.. 12.5 12.7 

4 Beechwood Hybrid No. 87.. 14.2 13.7 

5 Beechwood Hybrid No. 202. 11.9 12.S 

6 Beechwood Hybrid No. 207. 13.2 13.6 

7 C. I. 3808 16.2 16.6 

8 C. I. 3846 14.2 15.6 

9 C. I. 3972 14.7 15.6 

10 C. I. 3980 16.4 17.5 

lie. I. 3988 16.7 17.0 

12 C. I. 4004 14.3 14.0 

13 Common Rye 17.3 18.5 

14 Dawson's Golden ChaiT 13.0 12.3 

15 Deitz 15.1 14.6 

16 Early Ripe 12.2 12.6 

17 Early Ripe No. 26 13.2 14.0 

18 Early Red Clawson 9.9 9.5 

19 Farmer's Friend 18.8 19.9 

20 Fulcaster 14.4 15.3 

21 Fultz (Archias) 12.2 13.0 

22 Gold Coin 11.7 12.2 

23 Greene County 15.6 15.1 

24 Harvest King No. 7 13.4 14.2 

25 Harvest Queen 9.6 9.8 

26 Hicicman ?.8 812 

27 mini Chief 17.5 18.7 

28 Jones Climax 19.1 20.7 

29 Kanred 21.0 22.7 

30 Kessinger 18.0 19.3 

31 Kharkov 18.9 20.1 

32 Leap's Prolific 14.2 14.8 

33 Mediterranean No. 8 9.1 9.5 

34 Michigan Amber 10.7 11.3 

35 Michigan Amber (Indiana) 17.0 17.9 

36 Michigan Amber No. 7 ... 10.5 10.8 

37 Michigan Amber No. 12 . . . 9.3 9.3 

38 Michigan Wonder 10.9 11.1 

39 Michigan Wonder No. 4 ... 12.4 12.7 

40 Michigan Wonder No. 8 ... 10.8 11.0 

41 Michigan Wonder No. 21 . . 8.2 8.7 

42 Michigan Wonder No. 53 . . 8.5 9.6 

43 Michigan Wonder No. 54 .. 11.3 10.7 

44 Michigan Wonder No. 83 . . 13.6 13.7 

45 Michigan Wonder No. 96 . . 9.7 9.7 

46 Michigan Wonder No. 103 . 9.7 9.1 

47 Michigan Wonder No. 116 . 16.4 15.8 

48 Michigan Wonder No. 130 . 14.3 14.2 

49 Michigan Wonder No. 140 . 12.3 12.7 



Average yield 
Planting 3 Interior 5 

number Variety Rows Rows 

50 Michigan Wonder No. 141 . 10.7 10.3 

51 Michigan Wonder No. 155 . 10.1 9.8 

52 Michigan Wonder No. 209 . 12.1 12.5 

53 Michigan Wonder No. 211 . 9.9 9.9 

54 Michigan Wonder No. 221 . 11.0 11.1 

55 New York 123-32 17.2 17.5 

56 Niagara 13.8 13.5 

57 Nigger 11.8 11.8 

58 Old Ironclad 12.5 13.2 

59 Poole 10.5 10.7 

60 Poole No. 3 11.7 11.0 

61 Poole B-3 12.5 13.3 

62 Portage 15.9 17.3 

63 Pride of Indiana 14.2 14.4 

64 Pride of Genessee 15.7 18.1 

65 Reliable 12.6 12.9 

66 Red Cross 13.1 13.1 

67 Red May i4.8 14.8 

68 Red Rock (Indiana) 18.7 19.7 

69 Red Rock (Michigan) 7.5 6.8 

70 Red Wave 12.9 12.7 

71 Rochester Red 12.7 12.9 

72 Rosen Rye 20.7 24.0 

73 S. P. I. 11616 10.3 10.9 

74 S. P. I. 26012 13.4 12.9 

75 S. P. I. 26013 15.2 15.5 

76 S. P. I. 26014 17.5 18.8 

77 S. P. I, 26015 13.2 13.4 

78 S. P. I. 26017 13.4 13.5 

79 S. P. I. 26018 13.6 13.6 

SOS. P. I. 26019 11.6 11.6 

81 S. P. I. 26022 10.6 10.1 

82 S. P. I. 26023 9.1 8.5 

83 S. P. I. 26025 12.3 13.1 

84 S. P. I. 26029 15.4 15.6 

SS S. P. I. 26085 13.2 13.3 

86 Treadwell 12.7 12.8 

87 Valley 12.4 12.1 

88 Velvet Chaff No. 2 14.1 12.8 

89 Velvet Chaff No. 8 9.0 9.3 

90 Ziegler's Fly Proof 10.9 11.7 

91 13U-4a 14.1 13.9 

92 37a-4 14.6 14.7 

93 Fulcaster (Co-op) 17.4 18.5 

94 Fultz (Co-op) 15.2 15.9 

95 Kanred (Co-op) 19.1 20.6 

96 Poole (Co-op) 19.4 21.0 

Mean 13.4 13.8 



Experiments in Field Plot Technic 



17 



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18 Missouri Agr. Exp, Sta. Research Bulletin 49 

Work of 1921. — In 1920-21 ninety-six varieties of wheat 
were again tested by this method. Many of the varieties were the same 
as those tested in the preceding year, about 20 varieties being ehminated 
and a corresponding number added. The planting plan was the same 
as that of the preceding season. Poole wheat was used as a check 
variety. The wheat was drilled at the rate of 5 pecks per acre, October 
6, in rows running east and west. The season was favorable, but 
yields were reduced by the very rapid ripening of the wheat caused by 
the hot dry weather in the second and third weeks of June. The yields 
are shown in Table 5. 

TABI.E 6. — Yields of Wheat Varieties and Mixtures 
In Bushels per Acre. 1921. 



Planting 




Average yield 


number 


Variety 


3 Interior Rows 


5 Rows 


1 


Fulcaster 


17.3 


18.6 


2 


Harvest Queen 


14.2 


14.5 


3 


Mixture No. 1 (1, 2, 4, 5) 


15.9 


16.2 


4 


Michigan Wonder 


16.8 


17.8 


5 


Nigger 


10.8 


10.8 


6 


Michigan Wonder No. 31 


19.8 


30.8 


7 


Michigan Wonder No. 54 


18.9 


19.3 


8 


Mixture No. 2 (6, 7, 9, 10) 


20.8 


21.3 


9 


Michigan Wonder No. 96 


18.5 


18.9 


10 


Michigan Wonder No. 209 


21.7 


22.6 


11 


Beechwood Hybrid No. 12 


17.4 


18.8 


12 


Beechwood Hybrid No. 85 


16.5 


17.3 


13 


Mixture No. 3 (11, 12, 14, 15) 


17.6 


18.4 


14 


Beechwood Hybrid No. 87 


19.9 


19.9 


15 


Beechwood Hybrid No. 207 


17.4 


17.9 


16 


Michigan Wonder No. 221 


18.6 


20.3 


17 


Kanred 


13.6 


13.8 


18 


Mixture No. 4 (16, 17, 19, 20) 


17.8 


18.0 


19 


New York 123-32 


19.6 


19.7 


20 


Red Rock 


17.6 


17.4 


21 


Red Hussar 


16.3 


17.8 


22 


Turkey (Kansas) 


10.8 


10.5 


23 


Mixture No. 5 (21, 22, 24, 25) 


15.7 


15.9 


24 


Michigan Amber 


19.2 


19.6 


25 


Nigger 


14.1 


13.4 


26 


Fulcaster (Co-op) 


20.4 


21.2 


27 


Fulcaster (Outl) 


20.1 


20.6 


28 


Mixture No. 6 (26, 27, 29, 30) 


20.1 


21.0 


29 


Fulcaster (Blazier) 


20.6 


21.5 


30 


Fulcaster (Cowles) 


20.6 


20.6 




Mean 


17.6 


18.2 



Experiments in Field Plot Technic 



19 



On another field in 1921, a test of mixtures of varieties and 
strains of wheat in comparison with their pure constituents was con- 
ducted. Each mixture was made up of four varieties or strains, in 
equal quantities of seed by weight. The composition of the mixtures 
and the yields obtained are shown in Table 6. The planting plan is 
shown in figure 4. This wheat was drilled at the rate of 5 pecks per 



on I 



Ch26 



27 



28 



29 



30 



Cf\j6 



n 



16 



13 



20 



a 



12 



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/4 



IS 



Cfid 



Cli 



10 



CH 



s 



CKzi 



22 



23 



2f 



25 



CH 



16 



17 



IB 



19 



20 



CH 



B 



CH 



IZ 



13 



li 



15 



a 



/O 



Cnse 



27 



28 



29 



30 



CK 



8/ 



22 



23 



24 



2SCKd 



CH 



16 



n 



16 



19 



20 



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CH26 



27 



28 



29 



dO 



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B 



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Zi 



zz 



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17 



18 



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ZO 



CH 



10 



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CH 



21 



SZ 



23 



24 



25 



CHll 



12 



13 



14 



l3 



CH 



/o 



CHB 



Figure 4. — Planting Plan of Wheat Mixture Test 1021. Legend: B, 
border. CK, check. Numbers 1-30, planting numbers of varieties and mixtures 
tested, as given in Table G. 

acre in rows running north and south, on October 8, 1920. This test 
will be referred to as the wheat mixture test. 

In 1921 tests of oats varieties and of oats strains were also con- 
ducted in 5-row blocks. Thirty-two strains of Red Rustproof, in- 
cluding many of those tested in 1919 and a number of others, and 32 
strains of Kherson oats, obtained in the same way, were included in 
the oats strain test. The Kherson and Red Rustproof strains were 
arranged alternately, and both Kherson and Red Rustproof checks 
were grown, as shown in figure 5. The test of these 64 strains, in 
four series, occupied 16 ranges. The next eight ranges on the same 
plot were used for an oats variety test in which 32 varieties of oats 
were compared, each in four replicate plots. In this part of the field 
the Kherson and Red Rustproof check plots were continued. There 
are thus available the yields of 120 plots each of Kherson and Red 
Rustproof oats, or five strips of 24 plots of each arranged in pairs 
side by side. In both of these experiments the rows ran east and 
west, and were 18 feet long, cut to 16 feet in harvesting. The oats 
were drilled on March 12, at the rate of 10 pecks per acre. The yields 
of oats, particularly of the later-maturing varieties, were materially re- 
duced by the hot dry weather in the middle of June. The yields of the 
oats varieties are shown in Table 7, and those of the strains in Table 8. 



20 



Missouri Agr. Exp. Sta. Resicarch Bui.letin 49 



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Figure 5.— Planting Plan of Oats Variety and Strain Tests 1931. 
Legend: B, border. K, Kherson check. R, Red Rustproof check. Numbers 
1-64, planting numbers of oats strains, as given in Table 8. Numbers 65-96, 
planting numbers of oats varieties, as given in Table 7. 



Experiments in Field Plot Technic 21 



Table 7.— Yields of Oats Varieties. 
In Bushels per Acre. 1921. 

Planting Average yield 

number Variety 3 Interior Rows 5 Rows 



65 


Burt 


66 


Canadian 


67 


C. I. 603 


68 


Culberson 


69 


Danish Island 


70 


Early Dakota 


71 


Early Gothland 


73 


Carton 748 


73 


Green Russian 


74 


Irish Victor 


75 


Joanette 


76 


Fulghum 042 


77 


Monarch 


78 


Monarch Selection 


79 


Scottish Chief 


80 


Silvermine 050 


81 


Silvermine Selection 


82 


Sparrowbill (C) 


83 


Sterilis Selection 


84 


Storm King 


85 


Swedish Select 057 


86 


Fulghum 065 


87 


Fulghum 0113 


88 


Silvermine 0115 


89 


Silvermine 0117 


90 


Fulghum 0124 


91 


Fulghum 0145 


93 


Fulghum 0149 


93 


Fulghum 0151 


94 


Fulghum 0152 


95 


Silvermine 0165 


96 


Swedish Select 0165 




Mean 



49.13 


51.94 


25.31 


25.13 


22.50 


23.06 


24.75 


25.13 


19.69 


19.13 


21.56 


21.56 


23.44 


22.13 


21.00 


20.81 


26.06 


26.25 


29.81 


32.06 


19.31 


19.69 


45.19 


47.44 


29.63 


31.88 


35.63 


36.38 


26.63 


27.38 


31.69 


32.06 


22.13 


24.94 


15.38 


14.63 


38.63 


36.94 


20.06 


17.63 


21.00 


19.50 


42.00 


44.81 


42.00 


45.38 


25.13 


24.94 


21.75 


22.69 


45.38 


48.38 


39.19 


41.81 


42.75 


47.06 


39.75 


43.88 


39.75 


42.38 


28.31 


26.81 


20.81 


18.56 


29.85 


30.70 



22 



Missouri Agr. Exp. Sta. Research Bulletin 49 



Table 8. — Yields of Oats Strains (Red Rustproof and Kherson). 
In Bushels per Acre. 1921. 



Planting 
number 


^ed Rustproc 
Strain 


f strains 

Average 

Interior 

Rows 


yields 
5 
Rows 


Planting 
Number 


Kherson strains 
Average 
3 Interior 
Strain Rows 


yields 

5 
Rows 


1 


066 


24.00 


23.25 


2 




023 


35.25 


36.38 


3 


067 


24.00 


21.75 


4 




040 


36.57 


37.50 


5 


068 


23.25 


23.44 


6 




041 


36.56 


38.81 


7 


069 


19.31 


18.00 


8 




053 


38.06 


38.81 


9 


072 


18.38 


18.75 


10 




053 


39.75 


42.00 


11 


074 


22.31 


20.63 


12 




079 


32.63 


34.88 


13 


075 


24.19 


22.13 


14 




080 


35.44 


38.25 


15 


0118 


16.50 


16.31 


16 




082 


40.88 


41.44 


18 


0119 


22.31 


21.38 


17 




083 


35.44 


38.25 


20 


0120 


21.19 


19.69 


19 




085 


38.25 


41.81 


22 


0122 


19.13 


17.81 


21 




086 


36.75 


37.69 


24 


0125 


21.00 


19.88 


23 


Mixture** 


33.75 


36.38 


26 


0126 


25.31 


22.50 


25 




088*** 


27.00 


27.56 


28 


0128 


20.44 


20.25 


27 




089 


30.94 


31.69 


30 


0129 


21.94 


21.56 


29 




090 


36.38 


38.06 


32 


0130 


21.75 


20.25 


31 




091 


30.19 


31.88 


33 


0131 


24.56 


23.25 


34 




094 


31.69 


33.56 


35 


0132 


17.63 


19.13 


36 




095 


38.81 


39.75 


37 


0133 


18.94 


18.75 


38 




096 


36.38 


38.06 


39 


0134 


16.50 


15.75 


40 




097 


31.31 


32.25 


41 


0135 


17.63 


15.65 


42 




098 


38.63 


39.19 


43 


0136* 


32.44 


33.19 


44 




099 


38.81 


38.25 


45 


0141 


21.94 


21.19 


46 




0100 


40.13 


42.75 


47 


0163 


13.88 


12.94 


48 




0155 


37.50 


38.63 


50 
52 


0169 
0181 


15.38 
19.88 


14.44 
18.00 


49 
51 




0157 
0158 


43.69 
34.69 


45.00 

35.25 


54 
56 


0182 
0183* 


19.88 
41.44 


19.13 
43.31 


53 
55 




0159 
0160 


33.38 
30.19 


33.94 
31.13 


58 0383 
60 0391 
62 0394 
64 0395 
Mean 


23.63 
29.44 
22.31 
23.25 
21.00 


24.00 
30.19 
21.56 
21.94 
20.12 


57 
59 
61 
63 


0161 
0162 
0167 
0174 
Mean 


34.69 
25.31 
40.69 
36.75 
35.79 


36.00 
25.69 
39.94 
38.25 
37.14 


*Not taxonomically Red Rustproof. Ex- 
cluded from average. 


**Mixture 
0174. 


of strains 


082, 094, 


0100, 










***Not 
eluded 


taxonomically KJierson. 
from average. 


Ex- 



Experiments in Field Plot Technic 23 

COMPETITION AS A SOURCE OF ERROR IN PRELIMINARY 

TESTS. 

Previous Investigation. — The possibility of error from competi- 
tion in single-row tests was noted by Montgomery" in 1913, in the 
following passage : 

"In 1908 it was observed that a certain strain of early wheat in a series 
of row plats made a very poor appearance at harvest time, while the same 
strain planted in centgeners made a much better comparative showing. Ap- 
parently the larger and faster growing strains on each side, the rows being 
only 8 inches apart, exercised some competitive effect. This effect of com- 
petition has been noted for two years since. Also in certain variety tests 
of oats, grown in row plats 10 inches apart, the same effect was noted. 
Exact data cannot be given on this point, as the results from the series of 
plats planted in 1909 and in 1910 for this purpose were seriously impaired 
by unfavorable conditions; but Table XVIII, giving results from adjacent 
row plats sown at different rates, shows that the 800-seed rate made a marked 
increase over the 700-seed rate, while in a similar series of blocks (Table 
XIX), sown at the same rate, this marked increase was not noted. Since the 
800-seed row was always adjacent to the 400-seed row, it may have had some 
advantage on this account. Danger from this source can probably be avoided 
if care is taken to plant only similar varieties in adjacent rows. Where the 
block plat is used this source of error is eliminated." 

Hayes & Arny* found considerable competition between rod-rows 
grown one foot apart. Three-row plots were used in variety tests of 
winter wheat, spring wheat, barley, and oats, and the yields of each 
row determined separately, in 1916. The comparative yield of the 
border rows in each plot was then correlated with the comparative 
height and yield of the adjacent rows. There was some effect on the 
yield of border rows due to the height of adjacent rows in the case 
of barley and winter wheat. The results were variable in different 
plots. In the case of oats the effect of height was rather obscure, and 
in the case of spring wheat it was not apparent. The yield of adjacent 
rows appeared to be of some importance in the barley tests and in 
some of the spring wheat tests. These results led to the adoption of 
3-row plots with discarded border rows for preliminary testing at 
the Minnesota Station. 

Love and Craig* in describing the methods used in cereal investiga- 
tions at the Cornell Station describe the single-row test and add : "In 
order to prevent any effect which may be caused by two unlike sorts 
growing together the different strains are arranged according to 
earliness and other characters so as to reduce this source of error to a 
minimum." 



24 



Missouri Agr. Exp. Sta. Re;search Bulletin 49 



Kiesselbach" ' has published rather extensive data on the compe- 
tition between adjacent rod-rows. In his experiments the crops were 
compared in alternating single-row plots and in alternating 5-row 
blocks, each replicated fifty times. In some cases the border rows of 
5-row plots were discarded. The deviation of the result in the test 
in single-row plots from that of the test in 5-row plots is regarded as the 
measure of the effect of competition. The comparative yields of va- 
rieties of wheat and oats in alternating single rows and in alternating 
5-row plots are shown in Table 9, from Kiesselbach\ 



Table 9. — Relative Yields oe Two Small Grain Varieties When Compared 
IN Alternating Rows and in Alternating 5-Row Plats (Kiesselbach). 



Wheat 


Oats 


Average yield of 


50 plats 


Average yield of 50 plats 


Year and 


Alternating 


Alternating 


Year and 


Alternating 


Alternating 


variety 


single rows 


5-row blocks* 


Variety 


single rows 


5-row blocks^ 




% 


% 




% 


% 


1913 






1913 






Turkey 


100 


100 


Kherson 


100 


100 


Big Frame 


107 


97 


Burt 


130 


113 


1914 






1914 






Turkey 


100 


100 


Kherson 


100 


100 


Big Frame 


85 


97 


Burt 


139 


101 


1913 






1913 






Turkey 


100 


100 


Kherson 


100 


100 


Neb. No. 


107 


107 


Swedish 


82 


77 


28 






Select 






1914 






1914 






Turkey 


100 


100 


Kherson 


100 


100 


Neb. No. 


63 


85 


Swedish 


89 


93 


28 






Select 







♦Yield based on 3 inner rows of 5-row plats in 1914. 

Kiesselbach also submits interesting data on the competition of 
pure line selections of the same variety. It might be supposed that 
such strains, being similar in varietal characteristics, would be little 
affected by competition, and could therefore be safely compared in 
single-row plots. The average relative yields of three strains of Turkey 
wheat in single rows and in blocks for two seasons, however, showed 
that the two better strains were favored approximately 20 per cent and 
15 per cent, respectively, at the expense of the poorer strain, in the 
single-row test. A strain which yielded 26 per cent more than an- 
other in the single-row test yielded only 6 per cent more in the block 



Experiments in Field Plot Technic 25 

test. Kiesselbach has therefore adopted the practice of testing such 
strains in 5-row blocks replicated ten times instead of in single-row 
plots. 

Love* has criticized these results because in some cases at least 
the rows ran east and west rather than north and south. He states 
that in experiments at Ithaca, New York, there is little competition be- 
tween varieties grown in single rows, when the rows run north and 
south. "In order to obviate any criticism of this method," he adds, "it 
might be well to follow the plan of arranging varieties so that late 
sorts are grown together and the earlier ones together. In other words, 
the different sorts could be so arranged that they grade into one another 
as regards yield, earliness, and the like." To this Kiesselbach" replies 
that in some of his competition studies the rows ran north and south 
and in others east and west, and that striking competition occurred in 
both cases. He adds that although error resulting from row compe- 
tition would undoubtedly be reduced by grouping varieties of sim- 
ilar growth habits together, it appears that varieties fairly similar 
in growth habit may vary for some reason in relative competitive qual- 
ity. 

Experimental Results. — Some further evidence on competition 
as a source of error in plot experiments is afforded by a study of the 
relative yields of border rows and interior rows in the 5-row blocks used 
in these preliminary tests. It should be remembered, of course, that the 
effect on yield would be decidedly greater in single rows exposed to com- 
petition on both sides than in these border rows, which compete with 
another sort on only one side. The extent of the error from compe- 
tition in such border rows is of interest in determining whether it is 
necessary to discard the border rows of small blocks. When 5-row 
blocks are used, even if the border rows are not discarded, the relative 
effect of competition is greatly reduced, since only two of the five 
rows are subject to varietal competition and these are exposed only 
on one side. If this results in reducing the error from competition to 
a low point, or if varieties can be so arranged as to give this result, 
it may be advisable in practice to harvest 5-row blocks entire, thus 
avoiding the principal objection to the use of border rows — the loss of 
a considerable portion of the experimental area. 

Competition is particularly important as a source of error because 
of the fact that it tends to affect replicate plots similarly, and conse- 
quently does not necessarily increase plot variability. For this reason 
it is likely to escape detection, and, when it is involved in an experi- 
ment, its effect cannot be measured. There is no 'great objection to a 
considerable experimental error from plot variability in field experi- 



26 



Missouri Agr. Exp. Sta. Research Bulletin 49 



nients, if the experimenter determines the extent of the error and draws 
his conckisions accordin'gly. But a preUminary variety test in which 
error from competition is not controlled may be very nearly worthless 
as an indication of the relative value of varieties for field conditions, 
because actually the relative values of the varieties tested may frequent- 
ly differ by 50 or 100 per cent from the values determined in 
the test, without the slightest indication in the experimental results. 

Illustrations of Effects of Compe'tition. — The error from competi- 
tion may be illustrated by numerous examples from each of the eight 
tests here reported. An extreme case is the effect of competition on 
the relative yield of wheat and rye. Two varieties of rye, common 
rye and Rosen rye, were included in the wheat variety test, for com- 
parison with wheat. The average yields of Rosen rye and of the va- 
rieties of wheat adjoining it on either side, in interior rows and com- 
peting border rows of the four series, were as follows : 



Season Variety 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


1920. 
1921- 


'Niagara (Wheat) 

Rosen (Rye) 

Velvet Chaff No. 2 (Wheat 
■Red Hussar (Wheat) 

Rosen (Rye) 

Poole (ck) (Wheat) 


13.8 

20.7 

14.1 
14.3 

17.9 

11.8 


67 

100 

68 
80 

100 

66 


10.0 
'30.4 

[27.7 
9.8 

11.6 

fig.? 

[25.4 
11.2 


33 
100 

100 
35 

59 
100 

100 
44 



The disturbance of the true comparative value of the varieties 
by competition may be determined by comparing their relative yields 
in interior rows and in border rows. Thus Niagara wheat in 1920 
yielded 67 per cent as much as Rosen rye in plots protected from com- 
petition, but only 33 per cent as much in rows not protected from 
competition. Similarly the yield of Velvet Chaff No. 2 wheat was re- 
duced from 68 per cent to 35 per cent by competition with Rosen rye. 
In the following season the reduction in yield of the two varieties of 
wheat adjoining Rosen rye (Red Hussar and Poole) was not so 
great, but was still decidedly significant. This clear case of compe- 



Experiments in Field Plot Teciinic 



27 



tition serves to illustrate the phenomenen, although the competition 
between wheat and rye has little significance in itself as regards va- 
riety tests in general, since wheat and rye are not commonly included 
in the same test. 

Ordinarily the competition between varieties of the same crop 
is not so extreme. There are, however, a number of cases in which 
a variety of wheat or oats profited almost as extremely in competition 
with other varieties of the same crop as did the rye in competition 
with wheat in the cases cited above. The wheat variety, Michigan 
Wonder No. 116, which grew between two other wheat varieties, 
Leap's Prolific and Poole Selection, in 1921, gave the following results, 
as an average of the four series : 





Yield in 


Yield in competing 


Variety 


interior rows 


border 


rows 




Bushels 


Relative 


Bushels 


Relative 


Leap's Prolific 


14.9 


91 


9.9 

ri8.8 


53 
100 


Michigan Wonder No. 116 


16.4 


100 


\ 

[21.7 


100 


Poole Selection 


15.3 


93 


11.5 


53 



The efifect of competition in this case is almost as pronounced 
as in the case of the rye, although the three wheat varieties concerned, 
when protected from competition, gave almost equal yields and differed 
little in date of heading, date of maturity, and height. In this case 
a small difference in actual value between the varieties, as indicated 
by their yields when protected from competition, is greatly increased 
when their yields in adjacent single rows are compared. 

A striking case of competition in the oats variety test of 1921 was 
that of the three varieties Sterilis Selection, Fulghum, and Kherson, 
the check variety. Their average yields were as follows : 





Yield in 


Yield in competing 


Variety 


interior rows 


border rows 




Bushels 


Relative 


Bushels 


Relative 


Sterilis Selection 


38.63 


99 


28.50 

("48.75 

< 


58 
lOO 


Fulghum 


39.19 


100 










42.94 


100 


Kherson (check) 


40.69 


104 


34.18 


70 



28 



Missouri Agr. Exp. Sta. Research Bulletin 49 



These three varieties, which gave almost equal yields in rows 
protected from competition, differed decidedly in their yields in ad- 
jacent rows. Although Kherson outyielded Fulghum 4 per cent in 
plots protected from competition, its yield was 30 per cent less than 
that of Fulghum in single rows not protected from competition. 

Extreme effects of competition were shown in very numerous 
cases in the tests of Kherson and Red Rustproof strains in 1921. An 
example from this plot is the following: 



Strain 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


0169 (Red Rustproof check) 
067 (Red Rustproof) 
085 (Kherson) 


18.38 
24.00 
38.25 


77 
100 
159 


22.31 
ri8.75 

[17.44 
51.94 


119 
100 

100 
298 



The extreme advantage of the Kherson strain in competition with 
the Red Rustproof, increasing its margin of superiority from 59 per 
cent to 198 per cent, is particularly striking. Probably even more 
significant is the effect of competition between the two Red Rustproof 
strains, resulting in the conversion of a 23 per cent loss to a 19 per 
cent gain. 

All of the cases cited above are taken from plots in which the 
rows ran east and west. Some examples of varietal competition from 
tests in rows running north and south are the following: 

In the barley variety test, the variety Featherston 1118 occurred 
between Red River 973 and Oderbrucker (the check variety). The 
average yields of these three varieties in the three series were as follows : 



Variety 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


Red River 973 
Featherston 1118 
Oderbrucker (ck) 


27.25 
28.25 
34.87 


96 
100 
123 


31.20 
("24.60 

[25.65 
42.19 


127 
100 

100 
164 



Experiments in Field Plot Technic 



29 



In this case the advantage of Oderbrucker over Featherston was 
almost tripled by competition, and Red River, which yielded less than 
Featherston in the interior rows, excelled it materially in yield in the 
border rows. 

The oats varieties tested in rows running north and south in 1919 
showed marked effects of competition in several cases. The follow- 
ing will serve as an example : 



Variety 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


Kherson Selection 
Fulghum 042 
Lincoln 


61.3 
57.1 
50.3 


111 
100 

88 


84.7 
[49.4 

[50.7 
57.5 


171 
100 

100 
113 



In this case Lincoln, yielding 12 per cent less than Fulghum in in- 
terior rows, yielded 13 per cent more than Fulghum in border rows; 
while the advantage of Kherson Selection over Fulghum was in- 
creased from 11 per cent to 71 per cent. 

Marked competition is hardly to be expected in the oats strain test 
of 1919, regardless of the direction of the rows, because of the sim- 
ilarity of the strains in varietal characters. Three strains which proved 
to be taxonomically unlike Red Rustproof were included in this test, 
and each of these shows clearly the effects of competition. For ex- 
ample, strain 0124, which was classified as Fulghum, gave the follow- 
ing yields in comparison with the adjoining strains, 0127, classified as 
Kherson, and 0133, classified as Red Rustproof: 



Strain 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


01j'27 (Kherson) 
0124 (Fulghum) 
0133 (Red Rustproof) 


38.55 
63.90 
48.00 


60 
100 

75 


32.40 
'66.83 

78.75 
43.20 


48 
100 

100 
55 



30 



Missouri Agr. Exp. Sta. Re;se;arch Bulletin 49 



Moreover, the Red Rustproof strains showed competitive effects 
among themselves to some extent, though not so conspicuously as dif- 
ferent varieties. For example the strains 0122 and 0123, which were 
taxonomically identical, yielded as follows : 



Strain 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


0122 (Red Rustproof) 

0123 (Red Rustproof) 


47.85 
53.55 


89 
lOO 


55.13 

49.28 


112 
100 



Strain 0122 which was apparently 11 per cent inferior to strain 
0123 in the yields of interior rows, appeared to be 12 per cent superior 
to the same strain in the yields of their adjacent border rows. 

In the wheat mixture test of 1920 also the rows ran north and 
south. An example of competition from this test is the following: 



Variety 


Yield in 
interior rows 


Yield in competing 
border rows 




Bushels 


Relative 


Bushels 


Relative 


Poole (check) 

Michigan Wonder No. 221 

Kanred 


15.1 
18.6 
13.6 


81 
100 

73 


14.5 
'24.2 

21.4 

12.5 


60 
100 

100 

58 



In this case also differences in yield were increased by compe- 
tition. 

The individual cases cited above will serve to show the existence 
of competition as a source of error in these tests. As a result of 
competition the differences between varieties may be increased or de- 
creased, and in some cases a material advantage in yield may be con- 
verted to a material disadvantage. The phenomenon occurs, under 
conditions at Columbia, whether the rows run north and south or 
east and west. Of course it is not true that all of the difference in 
yield between border rows and interior rows is necessarily caused 
by varietal competition. Some variation in the yield of adjacent rod- 
rows will occur regardless of competition. When the means of only 



Experiments in Field Plot Technic 31 

four determinations are compared the effect of this variability may be 
considerable. If a field uniformly seeded to a single strain were har- 
vested in rod-rows and assumed to be made up of several different 
varieties each in four distributed plots, doubtless the average border 
yield would differ materially from the average interior yield in several 
"varieties." It is not however, likely, that such differences as those 
cited above would be caused by chance variability. Nevertheless, no 
final conclusions regarding competition as a source of error should be 
drawn from such individual cases. The extent of error from compe- 
tition is better shown in the average differences between border yields 
and interior yields, and in the mean coefficients of competition for 
complete tests. They are given in the next section. 

Relation of Competition to Various Characteristics of the Com- 
peting Varieties. — It is essential that competition be eliminated by the 
use of border rows, or counteracted by some such means as grouping 
varieties. The latter is decidedly the preferable method, from the 
standpoint of economy, if satisfactory results may be obtained by its 
use. But competition cannot be effectively controlled by grouping 
varieties unless there is a close correlation between competitive value 
and some character like earliness or height, which may be known in 
advance. Determinations of the correlation between competitive ef- 
fects and various characteristics of the varieties have therefore been 
made for each of the tests. The preliminary determinations were made 
as follows : 

(1) The average yield in interior rows and the average yield 
in the border rows on each side for all replicate plots of each variety 
or strain was determined. The replicate plots thus averaged were 
grown between the same varieties in each series, and it may be assumed 
therefore that their border rows were subject to the same competition. 
In the following discussion of competition each individual case repre- 
sents the mean of all the replicate plots of the test in question. For 
example, when it is stated that the correlation between competition 
and yield is determined in a test in which one hundred cases of compe- 
tition are involved, each of the hundred cases represents the mean of 
three or four determinations in replicate plots. In most cases the 
number of replicate plots was four. In the barley test of 1919 only 
three series were grown, and in the oats variety test of 1919, though 
four series were grown, only three could be used because one border 
row of each variety in the first series was harvested for seed and 
laboratory material. 

(2) Corresponding average yields were determined for check 
plots, those adjoining the same variety being averaged together. For 



32 Missouri Agr. Exp. Sta. Research Bulletin 49 

example, in the wheat variety test diagrammed in figure 1 the four 
check plots which adjoined variety 1 (one in each series) were aver- 
aged together, the four adjoining variety 2, the four adjoining variety 
3, etc. The four check plots adjoining varieties 89, 90, 91, etc. were 
similarly averaged. 

(3) The average yield of each border row for each variety was 
converted to the percentage of the average yield of the same variety 
in its interior rows. These yields of border rows in percentage will 
be referred to as "relative border yields." The relative border yield 
gives a rough indication of the effect of competition on the variety. 
When it is above 100, the variety yielded more in border rows (subject 
to competition) that in interior rows (protected from competition). 
When it is below 100, the border yield was less than the interior yield, 
in proportion. 

(4) An approximate measure of the competition between each 
pair of adjacent varieties was obtained by dividing the higher relative 
border yield by the lower, in the case of their adjacent border rows, 
and substracting 100 from the result. When the variety on the left 
has a higher relative border yield, this is given a positive sign; in the 
reverse case a negative sign. This figure is simply the predominance 
of the more strongly competing variety over the other in percentage of 
relative border yield. It will be referred to, for convenience, as the 
coefficient of competition. 

(5) This measure of competition was correlated with various 
characteristics of the competing varieties, including the relative yields 
in interior rows, the relative grain-straw ratios, the relative dates of 
heading and of maturity, and the relative heights. In correlating com- 
petition with the relative yield of the interior rows, the relative yield 
was determined by dividing the higher yield by the lower, subtracting 
100, and assigning a positive or negative sign, as before. The correla- 
tion determined, therefore, is the correlation between the percentage 
advantage of one variety over another in competition, and the differ- 
ence in yield of the two varieties, expressed in percentage, when pro- 
tected from competition. Relative grain-straw ratios were determined 
similarly, the ratios being first obtained by dividing the yield of straw 
by the yield of grain. Relative dates of heading and maturity and 
relative heights were determined simply by subtracting the value for 
one variety from the value for the other. In each case, of course, the 
sign was determined in the same way. 

A simple example explained in detail may serve to make this 
method clear. In the wheat variety test of 1921 the varieties Fultz 
(Bayer), Michigan Amber, and Michigan Wonder No. 211 occurred 



Experiments in Field Plot Technic 



33 



in the order named in four distributed sections of the field. The aver- 
age yields of these varieties in the four series, in bushels per acre, for 
border rows and for interior rows, are shown below, together with 
the average dates of heading, dates of maturity, and heights, also de- 
termined for the four series. 





23. Fultz (Bayer) 


39. Michigan Amber 


55. Michigan Wonder 
No. 211 




Row 
1 


Row 

2, 3, 4 


Row 

5 


Row 

1 


Row 

2,3, 4 


Row 

5 


Row 
1 


Row 

2,3,4 


Row 
5 


Average 
yields 


10.8 
bu. 


12.2 
bu. 


13.1 
bu. 


13.3 
bu. 


14.9 
bu. 


14.S 
bu. 


19.8 
bu. 


18.1 
bu. 


19.4 
bu. 


Average 
flate of 
heading 




21* 






21* 






19* 




Average 
date of 
maturity 




47* 






48» 






47* 




Average 
height 




43 in. 






42 in. 






43 in. 





* Dates of heading and maturity are the numbers of days after April 30. Thus 1 is 
May 1, 32 is June 1, 47 is June 16, etc. 



Now dividing the yields in border rows by the yields of the same 
varieties in interior rows, we obtain the relative border yields, which 
are substituted in the table below for the border yields in bushels. 
To determine the degree of competition between the varieties Fultz and 
Michigan Amber we divide the larger relative border yield (107) by the 
smaller (89) and subtract 100, giving 20 per cent. Since in this case the 
relative border yield of the variety on the left is higher, the difference is 
given a minus sign. Similarly a value of +12 per cent is obtained for 
the competition between Michigan Amber and Michigan Wonder No. 
211. These figures mean that the relative border yield of Fultz ex- 
ceeded that of Michigan Amber by 20 per cent in their competing 
border rows, while that of Michigan Wonder exceeded that of Michi- 
gan Amber by 12 per cent. 

The relative yields of these varieties are obtained similarly, — 
in the first case by dividing 14.9 by 12.2 (-|-22%) and in the second 
case by dividing 18.1 by 14.9 (+21%). Both values are positive be- 
cause in each case the yield of the variety on the left is higher than 
that of the variety on the right. The difference in dates of heading, 
maturity, and height are obtained simply by subtraction, being positive 
when the value of the variety on the right is greater and negative when 



34 Missouri Agr. Exp. Sta. Research Bulletin 49 

the value of the variety on the left is greater. The figures ready for 
correlation study will then appear as follows : 





23. Fultz 
(Bayer) 
Row Row Row 

1 2,3,4 5 


Compe- 
tition 
data 


39. Michigan 
Amber 
Row Row Row 
1 2, 3, 4 5 


Compe- 
tition 
data 


55. Michigan Wonder 

No. 211 

Row Row Row 

1 2,3,4 5 


Average 
yield 


89 


12.2 


107 


-20% 
+22% 


89 


14.9 


97 


+ 12% 
+21% 


109 


18.1 


107 


Average 
date of 
heading 




21 









21 




-2 




19 


1 


Average 
date of 
maturity 




47 




+ 1 




48 









47 




Average 
height 




43 




-1 




42 




+ 1 




43 





The columns headed "competition data" show the relation of the 
effect of competition to the yield, earliness, and height of the competing 
varieties. For example, Michigan Amber was at a disadvantage of 20 
per cent in competition with Fultz, though it was 22 per cent superior 
in yield when protected from competition. It headed the same day, 
matured one day later, and was one inch shorter. After correspond- 
ing data had been prepared for all the 96 varieties in this test, correla- 
tion tables with the coefficient of competition as subject and relative 
yield, date of heading, date of maturity, and height as relative were 
constructed. Correlations were determined similarly in the other tests. 
One of these correlation tables is shown in figure 6. In general, merely 



—40 


to —60 


—20 


to —40 





to —20 





to 20 


20 


to 40 


40 


to 60 


60 


to 80 




Total 



I I I 



1 


1 


1 


1 


1 
























1 












2 


1 


1 


2 


4 


2 


2 














1 


1 


7 


10 


5 


2 












1 


2 


6 


10 


8 


3 


5 














2 


3 


4 


11 


2 


1 


1 










1 




1 
1 




1 


3 

1 





20 26 21 16 8 



1 

14 

26 

35 

24 

5 

3 

112 



Figure 6. — Correi.ation Between Coefeicient of Competition and Rela- 
tive YiEivD, IN Wheat Variety Test 1920. 

r= +.582 ± .043. 



Experiments in Field Plot Technic 35 

the coefficient of correlation and its probable error are given, for lack 
of space. 

In the barley variety test, 1919, the effect of competition was quite 
marked. The average yield of border rows differed from the average 
yield of interior rows by 11.13 per cent, and the mean coefficient of 
competition was 21.30 per cent. Attempts were made to correlate 
competition with relative date of heading, date of maturity, grain-straw 
ratio, and yield. The correlation coefficients determined are shown 
in Table 10, together with the mean differences between competing 



Table 10. — Correlation 


OF Competition With Various Characteristics in 




Barley Varety Test 1919. 




Character 


Mean difference be- 


Coefficient of correlation 




tween competing 


with competition 




varieties 




Date of heading 


4.0 days 


—.153 ±.120 


Date of maturity 


2.6 days 


—.063 ±.123 


Grain-straw ratio 


38.0% 


+.072 ±.122 


Yield 


52.3% 


+.442 ±.099 



varieties in the characters whose relation to competition was studied. 
Although none of these correlations is statistically significant, in 
the strictest sense, it is noticeable that the correlation between compe- 
tition and yield is much greater than any of the others, and is equal 
to about four and one-half times its probable error. There was ap- 
parently some tendency for the better yielding varieties to profit by 
competition with the poorer yielders. On account of the relatively 
small number of cases involved in this and the other 1919 tests, the 
probable errors are high, and a fairly high coefficient of correlation 

Table 11. — Correlation oe Competition With Various Characteristics in 
Oats Variety Test 1919. 



Character 


Mean difference be- 


Coefficient of correlation 




tween competing 


with competition 




varieties 




Date of maturity 


3.56 days 


—.456 ±.103 


Grain-straw ratio 


50.2% 


—.091 ±.129 


Yield 


53.5% 


+.314 ±.117 



may consequently fail to attain statistical significance. Such a co- 
efficient, while not establishing the correlation, by no means indicates 
that the correlation does not exist. 



36 Missouri Agr. Exp. Sta. Research Bulletin 49 

The oats variety test of 1919 also showed distinctly the effects 
of competition. The border rows in this test differed in yield from 
the interior rows by 12.78 per cent, on the average, and the mean 
coefficient of competition was 27.67 per cent. Correlations were de- 
termined for competition and relative yield, date of maturity, and 
grain-straw ratio. Unfortunately the dates of heading are not avail- 
able for all varieties in this test. The correlation coefficients are shown 
in Table 11. 

Again no correlations of statistical significance are found, but 
the relation of yield and earliness of maturity to competing strength 
is at least suggestive. There was a tendency for early and high-yielding 
varieties to profit by competition at the expense of later and lower-yield- 
ing varieties, but the number of varieties was too small to permit the 
drawing of positive conclusions. 

The oats strains grown on the same field showed much less strik- 
ingly the effects of competition. The mean difference in yield be- 
tween border rows and interior rows in these 15 strains was only 6.50 
per cent and the mean coefficient of competition only 13.11 per cent. 
This is undoubtedly accounted for by the fact that the differences be- 
tween competing strains were so much less than in the oats variety 
test. When the three strains taxonomically unlike Red Rustproof are 
eliminated, leaving 12 strains of the same variety, the average devia- 
tion of border yields from interior yields is reduced to 4.69 per cent 
and the average coefficient of competition to 8.69 per cent. It is note- 
worthy that the competition between these strains of the same va- 
riety is decidedly less than that between different varieties. No sig- 



Table 12. — Correlation of Competition With Various Characteristics in 
Oats Strain Test 1919. 



Character 


Mean difference 


be- 


Coefficient of correlation 




tween competing 


with competition 




strains 






Date of heading 


2.67 days 




—.376 ±.136 


Date of maturity 


1.56 days 




— .244 ±.149 


Grain-straw ratio 


14.2% 




-i-.012 ±.159 


Yield 


17.1% 




-h.316 ±.143 



nificant correlation was found between these minor effects of compe- 
tition (for the 15 strains) and the relative time of heading, time of 
maturity, grain-straw ratio or yield, as is shown in Table 12, though 
in this case again the early strains and the high-yielding strains showed 
some tendency to profit by competition. 



Experiments in Field Plot Technic 37 

In the wheat variety test of 1920 the average yield of border rows 
differed from the average yield of interior rows by 12.30 per cent and 
the mean coefficient of competition was 19.79 per cent. These figures 
represent the average determinations when the two varieties of rye 
and the border yields of the varieties of wheat adjoining them were 
eliminated. The correlation between competition and relative yield, 
date of heading, and date of maturity were determined for this test 
and the coefficients of correlation are shown in Table 13. 

Table 13. — Correlation of Competition With Various Characteristics in 
Wheat Variety Test 1920. 



Character 


Mean difference be- 


Coefficient of correlation 




tween competing 


with competition 




varieties 




Date of heading 


2.3 days 


—.515 ±.048 


Date of maturity 


2.7 days 


—.552 ±.045 


Yield 


28.9% 


+.582 ±.043 



Competition in this test was negatively correlated with earliness of 
heading and maturity and positively with yield. All of the correla- 
tion coefficients are clearly significant. In other words, there was a 
rather pronounced tendency for the early and high-yielding varieties 
to profit in competition. To a considerable extent the early varieties 
were the high yielding varieties in this test, as indicated by the fact 
that the correlation coefficient for date of heading and yield was —.511 
±.051, and that for date of maturity and yield was —.642 ±.041. Al- 
though it is clear from these results that early, high-yielding varieties 
excelled in competition, it is not clear whether they did so chiefly as a 
result of their earliness or chiefly as a result of their yield. 

Table 14.— Correlation of Competition With Various Characteristics in 
Wheat Variety Test 1921. 



Character 


Mean difference be- 


Coefficient of correlation 




tween competing 


with competition 




varieties 




Date of heading 


2.1 days 


—.271 ±.060 


Date of maturity 


1.6 days 


—.222 ±.062 


Height 


3.3 inches 


-I-.347 ±.057 


Yield 


19.5% 


+.294 ±.059 



Similar results were obtained in the wheat variety test of 1921 
in which the difference between the average yield of border and in- 
terior rows was 12.89 per cent and the mean coefficient of competition 



38 Missouri Agr. Exp. Sta. REsii arch Bulletin 49 

was 18.85 per cent. Correlations were determined for competition and 
relative yield, date of maturity, date of heading, and height in this 
test. The coefficients of correlation thus determined are shown in 
Table 14. 

In this case, as in the wheat variety test of the preceding season, 
dates of heading and maturity were correlated negatively and yield 
was correlated positively with competition. The coefficients of correla- 
tion were materially lower, and in fact are hardly significant. It is in- 
teresting that in this case height was correlated more closely with 
competition than were either earliness or yield. In this season again 
earliness was correlated to some extent with yield, the coefficients of 
correlation, for date of heading and yield being — .331 ±.062 and for 
date of maturity and yield —.419 ±.057. 

In the wheat mixture test of 1921 the varieties were grouped 
roughly in respect to earliness, and in only three cases was there a 
greater difference than two days in heading or maturity between ad- 
jacent varieties. The rows in this test ran north and south. The 
conditions may be considered favorable in this test for the reduction 
of competition. Nevertheless the average yield of border rows dif- 
fered from that of interior rows by 10.07 per cent and the mean co- 
efficient of competition was 14.28 per cent. The coefficients of correla- 
tion determined for competition and date of heading, date of maturity, 
and yield, are shown in Table 15. 

Table 15.— Correlation of Competition With Various Characteristics in 
Wheat Mixture Test 1921. 

Character 



Mean difference be- ' 


Coefficient of correlatior 


tween competing 


with competition 


varieties 




L2 days 


—.514 ±.083 


0.8 days 


—.613 ±.070 


19.2% 


+ .554 ±.078 



Date of heading 
Date of maturity 
Yield 

In this test significant negative correlations between competition 
and dates of heading and maturity and a significant positive correla- 
tion between competition and yield are shown. The tendency for 
early, high-yielding varieties to profit by competition was about as 
strong as in the wheat variety test of the preceding season, though the 
extent of competitive effect was considerably reduced. 

The effects of competition in the oats variety test in 1921 were 
extreme. The yields of border rows differed by 16.74 per cent, on 
the average, from the yields of interior rows, and the mean coefficient 
of competition was 39.15 per cent. The extreme effects of compe- 



Experiments in Field Plot Technic 39 

tition in this test are probably accounted for by the fact that the va- 
rieties differed very widely in varietal type and in yield. Differences 
of as much as 17 days in date of heading, 13 days in date of maturity, 
and almost 200 per cent in yield, were involved. The correlations de- 
termined between competition and relative date of heading, date of 
maturity and yield, are shown in Table 16. 

Table 16. — Correlation of Competition With Various Characteristics in 

Oats Variety Test 1921. 

Character 



Mean difference 
tween competin 
varieties 


be- 
g 


Coefficient of correlation 
with competition 


4.8 days 
4.1 days 
51.1% 




—.648 ±.060 
—.860 ±.028 
-f.484 ±.082 



Date of heading 
Date of maturity 
Yield 

A remarkably high negative correlation between date of maturity 
and competition is shown. The negative correlation between date of 
heading and yield is also quite high, while the positive correlation be- 
tween yield and competition is barely significant. In this test, in which 
extreme differences in time of maturity occurred, the early-maturing 
varieties had a very distinct advantage in competition with the later 
varieties. Earliness was very closely correlated with yield in the oats 
variety test of this season, the coefficient of correlation for date of 
heading and yield being —.750 ±.052 and that for date of maturity and 
yield being —.894 ±.024. Considering the close correlation of earliness 
and yield, and the relatively low correlation of yield and competition, 
it would seem that the latter may be merely a by-product of the rela- 
tion of earliness to competition. Since the early varieties were the 
leaders both in competition and in yield, some correlation of yield and 
competition is inevitable. 

In the oats strains test of 1921 Kherson and Red Rustproof strains 
were alternated and both a Kherson and a Red Rustproof check were 
grown. In most cases therefore the competing border rows repre- 
sented these two varieties, though in some cases two Red Rustproof 
or two Kherson plots occurred together, as is shown in the planting 
plan in figure 5. The effects of competition in this plot were quite 
distinct, as is to be expected, though they were not so extreme as in 
the oats variety test discussed above, which was located on the same 
field. The average yield of border rows differed from the average yield 
of interior rows by 11.76 per cent. The mean coefficient of compe- 
tition was 23.85 per cent. 

When we exclude the competition between the three strains not 
true to name and the strains adjacent to each, that between the Kher- 



40 



Missouri Agr. Exp. Sta. Research Bulletin 49 



son and Red Rustproof check plots, and that between adjacent strains 
of the same variety, 58 cases of competition between different strains 
of Kherson and Red Rustproof remain. In these the mean yield of 
border rows differed from that of interior rows by 14.06 per cent and 
the mean coefficient of competition was 30.86 per cent. In every case 
the Kherson strain outyielded the adjacent Red Rustproof strain, 
though the advantage in yield varied from 27 per cent to 165 per cent. 
Similarly, the Kherson strains were earlier in maturity and heading, 
and taller, in each case, but with a rather wide variation in the extent 
of their advantage. In all but three of the 58 cases the Kherson strains 
showed a greater advantage in yield over the adjacent Red Rustproof 
strains in their competing border rows than in their interior rows. 
The average yields of the 30 Red Rustproof strains and 29 Kherson 
strains, in interior rows and competing border rows, were as follows : 





Average yield in 
interior rows 


Average yield in 
competing border 
rows 




Bushels 


Relative 


Bushels 


Relative 


Red Rustproof strains 
Kherson strains 


21.00 
35.79 


100 
170 


18.59 
41.00 


100 
222 



The Kherson strains outyielded the Red Rustproof strains by 70 
per cent in their interior rows and by 122 per cent in their competing 
border rows. The coefificients of competition, like the relative yield, 
earliness, and height, varied rather widely. Correlations were there- 
fore measured for the advantage of the Kherson strain of each adjacent 
pair in competition and its advantages in yield, date of heading, date 
of maturity, and height. The coefficient of correlation in each case 
was insignificant. 



Discussion. — In each of these tests, with the exception of the 
oats strain test of 1919, in which most of the strains compared be- 
longed to the same variety, border rows differed from interior rows in 
yield by more than 10 per cent. Differences as great as this will change 
materially the relative standing of varieties. In single-row tests the 
effects of competition would be considerably greater than in these 
border rows, affected by competition on only one side. Furthermore, 
in each test, of course, there were many cases in which competition 
caused much larger differences in yield than are shown by average 
figures. 



Experiments in Field Plot Technic 



41 



The relation of the direction of rows to the effects of varietal com- 
petition is not clearly shown by these experiments. The tests which 
showed least the effect of competition, the oats strain test of 1919 
and the wheat mixture test of 1921, were in rows running north and 
south. But relatively little effect from competition is to be expected 
in these tests, regardless of the direction of the rows, because of the 
similarity of adjacent strains. In the oats strain test 12 of the 15 
strains were taxonomically identical, and it has been shown that the 
effects of competition among these was much less than among the 
strains of diiferent varieties. In the wheat mixture test the varieties 
making up each mixture, which were grown side by side in the test, 
were chosen partly for their similarity in time of maturity, and the 
differences between adjacent varieties were therefore considerably 
less than in the wheat variety test of the same season. It cannot be 
stated definitely, therefore, from the results of these tests, that tests 
in rows running north and south are either more or less subject to error 
from competition than tests in rows running east and west. It is 
clear, however, that a considerable error from varietal competition 
may occur in tests in which the rows run north and south, as is evi- 
denced particularly by the barley and oats variety tests of 1919. 

The relation of competition to relative date of heading, date of 
maturity, grain-straw ratio, height, and yield, insofar as it was in- 
vestigated in these experiments, is shown in summary form in Table 
17. Although none of these characteristics shows a significant rela- 



Table 17. — Summary of Effects of Competition in All Tests. 



Test 







o . 




^s; 


H^^' 


1) u c 

•2'C rt 


" i! 


fa rti: 

3 >« 


s's t 








" " o 




§ 


27 


2L30 


24 


27.67 


15 


13.11 


94 


19.79 


94 


18.85 


30 


14.28 


32 


39.15 



Date of 
Heading. 



Coefficient of Correlation between Competition and — 



Date of 
Maturity. 



Grain- Straw 
Ratio. 



Height. 



Yield. 



Barley variety 
Oats variety 
Oats strain 
Wheat variety 
Wheat variety 
Wheat mixture 
Oats variety 



1919 
1919 
1919 
1920 
1921 
1921 
1921 



-.153 + .120 

— .376±.136 

— .5i5±.048 

— .271±.060 

— .514±.083 

— .648+. 060 



.063±.123 
.456±.103 
.244±.157 
.552±.045 
.222±.062 
.613±.070 
.860+. 028 



+ .072±.122 
— .091 + .129 
+ .012±.159 



+ .347±.057 



+ .442±.099 
+.314±.117 
+ .316±.143 
+ .582±.043 
+ .294±.059 
+ .S54±.078 
+.484±.082 



tion to competition in every case, the results of the tests are fairly 
consistent. The correlation of competition with yield is always posi- 
tive, and is fairly high in every case, the lowest coefficient being -|-.294 
±.059. From these results there can be no doubt that the higher yield- 
ing varieties are those which in general have profited by competition. 
The date of heading and the date of maturity show a negative correla- 



42 



Missouri Agr. Exp. Sta. Research Bulletin 49 



tion with competition in each case, though some of the coefficients 
are insignificant. It is clear therefore that early varieties are, in gen- 
eral, able to compete more strongly, but the extent of this relation is 
quite variable. The grain-straw ratio showed no significant relation 
to competition in any of the experiments of 1919, and was not deter- 
mined for the succeeding tests. Height was correlated positively with 
competition in the one test in which height was determined, the wheat 
variety test of 1921. In this test height was more closely related to 
competition than were date of heading, date of maturity, or yield. 

In the oats variety tests, the relation of early maturity to compe- 
tion is particularly marked, the coefficients of correlation in both oats 
variety tests being distinctly greater for date of maturity and compe- 
tition than for yield and competition. In the wheat tests there was 
little difference in the degree of relation to competition between earli- 
ness and yield. In the one test of barley varieties conducted, yield 
was more closely correlated with competition than was either the 
date of heading or date of maturity, but none of the three showed a 
clearly significant correlation. 

It is clear that in these trials the early, high-yielding varieties 
profited by competition. To a considerable extent these may be the 
same varieties, for the correlation of earliness and yield was high in 
most of the tests conducted. The relation of earliness and other 
characters to yield under Missouri conditions will be considered more 
fully in another paper, but data of interest in this connection are ap- 
propriate here. The coefficients of correlation of yield with date of 
heading and date of maturity in the variety tests discussed in this 
paper are shown in Table 18. 



Table 18. — CoRREivATioN OP Yield With Dates op Heading and Maturity in 
Variety Tests of Barley, Oats, and Wheat 



Number of 
Crop Season varieties 



Coefficient of correlation of 
yield with — 
Date of heading Date of maturity 



Barley 1919 27 

Oats 1919 40 

Oats 1921 32 

Wheat 1920 94 

Wheat 1921 94 



-.281 ±.120 

-.750 ±.052 
-.511 ±.051 
-.331 -+-.062 



— .271 ±.120 
—.627 ±.065 

— .894 ±.024 

— .642 ±.041 

— .419 ±.057 



When a very high correlation exists between earliness and yield 
it is likely that a character closely correlated with one may show a 
high degree of correlation with the other, which might not be shown 
were it not for the first correlation. For example, suppose earliness 



Experiments in Field Plot Technic 43 

of maturity is largely responsible for strong competitive value. Then 
in a season when earliness is closely correlated with yield a close cor- 
relation of competition and yield is likely to be found, not because high 
yield makes for strong competition but because the high-yielding va- 
rieties are early. Conversely, the competing value may be dependent 
on the yield and the correlation with earliness may be incidental, under 
the same conditions. If the relation of earliness and yield were con- 
stant, such a question would have little practical importance, but when 
the relation is reversed, as it may be in different localities and even in 
different seasons in the same locality, the relation of competition to 
the two characteristics may be very different. The relation of compe- 
tition to earliness and yield in these tests, therefore, may be due pri- 
marily to the predominating influence of either of these two charac- 
teristics, or to the influence of both. 

General conclusions regarding competition should not be drawn 
from these tests. The problem of competition is complicated by many 
factors, and will require numerous and extensive investigations for 
its solution. These results, however, indicate that gross errors from 
this source are commonly involved in variety tests, that such errors 
occur both in rows running east and west and in rows running north 
and south, that the error is less when the varieties and strains com- 
pared are structurally similar than when they are widely different, and 
that the error may be reducible to some extent by the grouping of va- 
rieties according to the time of maturity and possibly other characters, 
when the relation of such characters to competition is more fully 
studied. In the present state of knowledge regarding the relation of 
competition to the characteristics of the varieties compared, the use 
of border rows is highly desirable, since by their use the error from 
competition can be practically eliminated. 

SIZE AND REPLICATION OF PLOTS. 

Previous Investig-ation. — Most of the direct evidence reported 
on replication and size of plots has been obtained in experiments in 
which a field of a uniformly handled crop is harvested in a large num- 
ber of small sections. These sections are grouped to form plots of 
different shapes and sizes, and systematically distributed sections are 
averaged to represent replicate plots. The relative variability of the 
yields determined by each plot arrangement is the criterion of expe- 
rimental accuracy. Such experiments have been reported by Morgan" 
with wheat and fodder corn. Wood and Stratton" with mangels, Mer- 
cer and Hall " with wheat and mangels, Hall and Rusself with wheat, 



44 Missouri Agr. Exp. Sta. Re;se;arch Bulletin 49 

Montgomery"'" with wheat, Kiesselbach" with oats, and Day^ with 
wheat. 

The general conclusions drawn from these experiments are in 
harmony, though the specific size and shape of plot and number of 
replications found most desirable vary rather widely. In general, plot 
variabilit}' was reduced by increasing the size of the individual plot, 
up to a certain limit, but it was reduced much more effectively by rep- 
lication of plots. For a given area a large number of small plots was 
always found more accurate than a small number of large plots. 

But the size of the plot cannot be reduced indefinitely for several 
reasons. As the plot becomes smaller the proportion subject to "bor- 
der effect" rapidly becomes greater. This border effect may be due 
to the modified growth of plants adjoining an alley or to the in- 
fluence of the competition of different varieties in adjacent rows. If 
the borders are not discarded an important systematic error is involved ; 
if they are discarded a considerable portion of the land and labor is 
lost. In either case the disadvantage is increased as the size of the 
plot is decreased. When single rod-row plots are used the whole 
plot is subject to border effect. .The importance of this error has 
already been discussed. Another disadvantage of the extremely 
small plot is that slight differences in stand and small mechanical er- 
rors have a marked effect on the yields. The increased labor involved 
in handling a large number of small plots rather than a small number 
of large plots is also an important disadvantage. 

The length of the so-called rod-row has usually been determined 
by convenience. Commonly used lengths when the rows are a foot 
apart are 16 feet for wheat, 20 feet for barley, and 15 feet for oats, 
since with these lengths yields in grams per row may easily be con- 
verted to bushels per acre. In other cases the most convenient length 
is determined by the dimensions of experiment fields. Although in- 
creasing the length of the row would doubtless reduce variability, a 
greater gain could be made on the same area by further replication. 
Ordinarily it is preferable, therefore, to retain the most convenient 
length and to make any desired increase in size of plot in the width, 
for widening the plots will rapidly reduce the proportion subject to 
border effect. 

Experimental Results. —Size of Plots. — By comparing the stand- 
ard deviations of single rows and blocks consisting of three and five 
rows each, in the check plots, it is possible to determine the relative 
value of plots of the three sizes in counteracting plot variability. In 
this comparison the single-row and three-row plots correspond respec- 
tively to 3-row and 5-row plots in which the border rows are dis- 



Experiments in Field Plot Technic 



45 



carded, since they are made up of rows protected from varietal compe- 
tition by border rows. In each of the computations summarized be- 
low each check plot is represented by only one yield. For example, in 
determining the yield and standard deviation of single rows in the 20 
check plots of the oats variety test of 1919, the constants for single 
rows are the average of determinations made independently for Row 
2 of each of the 20 plots, for Row 3, and for Row 4. The determina- 
tions for 3-row plots are similarly made from the computed yields of 
the three interior rows of each check plot, and those for 5-row plots 
from the computed yields of the entire plots. Thus each determination 
represents the same number of plots and the same area, the only dif- 
ference being in the size of the individual plot. It would be possible, 
of course, to test 40 per cent more varieties with the same number of 
replications or to increase the number of replications by 40 per cent 
for the same number of varieties on the same area, if 3-row blocks 
were used rather than 5-row blocks. 

The yield and variability of check plots of different sizes in the 
barley variety test of 1919 are shown in Table 19. The variety grown 
in these check plots was Oderbrucker, seeded at the rate of 8 pecks 
per acre. The check variety was grown in every sixth plot. 



Table 19. — Yield and Variability of Check Plots. 
Single-row, Three-row, and Five-row — Barley Variety Test 1919. 





Number 


Yield 




Size of plot 


of plots 


per acre 


Standard deviation 






bu. 


bu. 


% 


Single-row 










Row 1 


21 


41.26 


7.95 


19.26 


Row 2 


21 


36.71 


8.30 


22.61 


Row 3 


21 


37.15 


8.48 


22.84 


Row 4 


21 


35.82 


10.37 


28.96 


Row 5 


21 


42.12 


11.86 


28.16 


Alean of three 










interior rows 


21 


36.56 


9.05 


24.80 


Mean of 










five rows 


21 


38.61 


9.39 


24.37 


Three-row Plot 










(Interior rows) 


21 


36.56 


8.11 


22.18 


Five-row Plot 












21 


38.61 


8.29 


21.47 



The variability of the single-row plots is 12 per cent higher on 
the average than that of the 3-row plots. That is, 3-row plots with 



46 



Missouri Agr. Exp. Sta, Research Bulletin 49 



borders discarded would have given in this case somewhat more va- 
riable results than 5-row blocks with borders discarded. The same 5- 
row blocks harvested entire (with borders retained) gave slightly less 
variable yields than when the borders were discarded. 

The same comparison may be made in the check plots of the 
oats variety test of 1919. The check variety was Red Rustproof, 
drilled at the rate of 10 pecks per acre in every ninth plot. The re- 
sults are shown in Table 20. 



TabIvE 20. — Yield and Variability of Check Plots. 
Single-row, Three-row, and Five-row — Oats Variety Test 1919. 





Number 


Yield 




Size of plot 


of plots 


per acre 


Standard deviation 


Single-row 
Row 1 


20 


bu. 
44.64 


bu. 
10.37 


23.23 


Row 2 


20 


47.97 


9.81 


20.45 


Row 3 


20 


46.56 


11.42 


24.53 


Row 4 


20 


46.95 


13.81 


29.41 


Row 5 
Mean of three 


20 


42.09 


11.58 


27.51 


interior rows 


20 


47.16 


11.68 


24.80 


Mean of 










five rows 


20 


45.64 


11.40 


25.03 


Three-row Plot 

(Interior rows) 
Five-row Plot 


20 

20 


47.16 
45.64 


10.62 

9.72 


22.59 
21.30 



The results in this case are practically identical with those of the 
barley variety test. Protected single rows were 10 per cent more va- 
riable than protected 3-row blocks, while the latter were only 6 per 
cent more variable than unprotected 5-row blocks. 

In the test of strains of Red Rustproof oats, conducted on the 
same field in 1919, adjoining the oats variety test, the same variety 
was used as check, and the crop was seeded on the same day with the 
same machine, but the check plots were in every sixth instead of every 
ninth plot. The corresponding data for these check plots are given in 
Table 21. 

Although the variability of these plots is lower, the relative va- 
riability of plots of different sizes is similar to that of the variety test. 
The single interior rows are on the average 24 per cent more variable 
than the 3-row block. The 3-row plot is only very slightly more va- 
riable than the 5-row plot. 



Experiments in Field Plot Technic 



47 



Table 31. — Yield and Variability oe Check Plots. 
Single-row, Three-row, and Five-row. — Oats Strain Test 1919. 





Number 


Yield 




Size of plot 


of plots 


per acre 


Standard deviation 






bu. 


bu. 


% 


Single-row 










Row 1 


18 


41.87 


6.35 


15.15 


Row 2 


18 


40.88 


5.52 


13.51 


Row 3 


18 


43.50 


5.81 


13.37 


Row 4 


18 


45.00 


7.31 


16.25 


Row 5 


18 


41.50 


6.37 


15.35 


Mean of three 










interior rows 


18 


43.13 


6.21 


14.38 


Mean of 










five rows 


• 18 


42.55 


6.27 


14.73 


Three-row Plot 










(Interior rows) 


18 


43.13 


5.04 


11.68 


Five-row Plot 












18 


42.55 


4.86 


11.41 



In the wheat variety test of 1920 the check variety was Fultz, 
which was seeded at the rate of six pecks per acre in every 
seventh plot. The results of interest in this connection are shown in 
Table 22. 



Table 22. — Yield and Variability of Checks Plots. 
Single-row, Three-row, and Five-row. — Wheat Variety Test 1920 





Number 


Yield 




Size of plot 


of plots 


per acre 


Standard deviation 






bu. 


bu. 


% 


Single-row 










Row 1 


80 


20.74 


6.58 


31.72 


Row 2 


80 


17.28 


5.03 


39.05 


Row 3 


80 


18.34 


4.50 


24.53 


Row 4 


80 


17.29 


5.10 


39.48 


Row 5 


80 


19.37 


6.00 


30.97 


Mean of three 










interior rows 


80 


17.64 


4.87 


37.68 


Mean of 










five rows 


80 


18.60 


5.44 


39.15 


Three-row Plot 










(Interior rows) 


80 


17.64 


4.43 


35.11 


Five-row Plot 












80 


18.63 


4.77 


35.60 



48 



Missouri Agr. Exp. Sta. Research Bulletin 49 



Again the single rows are distinctly more variable than the 3-row 
plot, in this case to the extent of 10 per cent. The 5-row and the 
3-row plots are about equally variable, the slight advantage in this case 
being in favor of the latter. 

To summarize, it is evident that the protected 3-row plot is some- 
what less subject to plot variability than the protected single-row, but 
the relative value of the 5-row plot harvested entire and the same plot 
harvested as a protected 3-row block is not clear. Some further 
comparison of these two methods was made in 1921. The variability 
of the check plots in both the wheat and oats tests was computed as 
protected 3-row and as unprotected 5-row plots. In the wheat tests 
the check variety was Poole, seeded at 5 pecks per acre in every 
seventh plot in the variety test, and in every sixth plot in the mixture 
test. In the oats tests the check variety was Kherson, seeded at 10 
pecks per acre in every sixth plot. The results are shown in Table 23. 



Table 23. — Yield and Variability of Check Plots. 
Three-row and Five-row. — Wheat and Oats Tests, 1921. 





Number 


Yield 






Size of plot 


of plots 


per acre 


Standard deviation 






bu. 


bu. 


% 


Wheat Variety Test 

Three-row Plots 


80 


14.89 


2.16 


14.50 


(Interior rows) 










Five-row Plots 


80 


13.98 


1.90 


13.61 


Wheat Mixture Test 










Three-row Plots 


30 


15.48 


3.25 


20.98 


(Interior rows) 










Five-row Plots 


30 


15.78 


3.55 


22.49 


Oats Variety and Strain Tests 

Three-row Plots 


120 


37.95 


4.61 


12.15 


(Interior rows) 










Five-row Plots 


120 


38.37 


4.70 


12.25 



In no case are the differences very great. The variability of 3-row 
blocks is slightly greater in the mixture test and that of 5-row blocks 
in the variety test of wheat. There is practically no difference between 
the two in the oats tests. 

Apparently there is no constant material gain in plot uniformity 
obtained by the inclusion of the border rows of the 5-row plot, even 
though the size of the plot is materially increased by this procedure. 
Even if variability were decreased by their inclusion, the practice would 
be of doubtful value in most tests, for the reasons given in the last 
section ; but with practically no decrease in variability there is left no 



Experiments in Field Plot Technic 49 

reason for the harvesting of these rows. They are not wasted because 
they are not harvested, for they serve a valuable purpose; the waste 
would be involved rather in harvesting them, for the added labor and 
expense would contribute nothing to the accuracy of the experiment. 

Although protected 3-row plots are less variable than protected 
single-row plots, they are not necessarily preferable. Three protected 
3-row plots require the same area as five protected single-row plots, 
and the harvesting of almost twice as large a crop (nine rows in the 
first case for every five in the second). If the mean yield of five 
single rows has as low a probable error as the mean yield of three 
3-row plots, the protected single-row plot will ordinarily be pre- 
ferable, because of the reduction of labor in harvesting and thresh- 
ing. When the standard deviation of the check plot yields is known, 
the probable error of the mean of any number of replicate plots can 
be computed and the number of replications for any given degree of 
accuracy determined. If single-row plots were 29 per cent more 
variable than 3-row plots, the probable errors of the mean of three 
3-row plots and of five single-row plots would be equal, since the prob- 
able error of the mean is equal to the probable error of a single deter- 
mination divided by the square root of the number of determinations, 
and since the square root of 5 is 29 per cent greater than the square 
root of 3.' In the cases herein cited the advantage of the 3-row plots 
was considerably less than 29 per cent in every case, and we may con- 
fidently expect therefore that protected single-row plots repeated five 
times will be less variable than protected three-row plots repeated three 
times, which would require the same area and more labor. 

Some further evidence on the relative variability of the protected 
3-row plot and the unprotected 5-row plot, or, in other words, of 
5-row plots, harvested with and without their border rows, may be ob- 
tained from the yields of the tested varieties and strains. Since the 
number of replications of each strain is small, average deviations are 
given instead of standard deviations. The inclusion of border rows in 
the 5-row plots should not increase variability, since the adjacent va- 
rieties are the same in each series, and the competitive effect should be 
no more variable than would be that of the same variety. A clear-cut 
comparison of 5-row and 3-row plots is therfore available in this case. 
In the case of the check plots this comparison was somewhat obscured 
by the competitive effect of different varieties on the border rows, which 
might be expected to increase variability and thus to conceal a possible 
advantage of the 5-row plot. 

The average variability of 3-row and 5-row plots in the strains 
tested in these experiments is shown in Table 24. In each case the 



50 



Missouri Agr. Exp, Sta. Resijarch Bulletin 49 



figur,e given is the mean of the average variabilities determined for all 
of the varieties or strains in the experiment. 



Table 24.- 



YiELD AND Variability of Test Plots. 
Three-row and Five-row. 





Season 


Number 
of vari- 
eties 


Ntmiber 
of Repli- 
cations 


Three-row Plots 


Five-row Plots 


Test 


Yield 

bu. per 

acre 


Average 
Devia- 
tion 

% 


Yield 

bu. per 

acre 


Aver- 
age 
Devia- 
tion 
% 


Barley varieties 


1919 


27 


3 


22.06 


15.35 


21.95 


15.44 


Oats strains 


1919 


15 


4 


50.07 


5.96 


50.20 


5.10 


Wheat varieties 


1920 


96 


4 


13.39 


24.27 


13.78 


24.36 


Wheat varieties 


1921 


96 


4 


15.42 


10.30 


15.57 


9.74 


Wheat mixtures 


1921 


30 


4 


17.62 


9.84 


18.15 


10.03 


Oats varieties 


1921 


32 


4 


29.85 


10.86 


30.70 


10.14 


Oats strains 


1921 


64 


4 


28.40 


10.82 


28.63 


10.58 



There is no consistent difference in variability between the 3-row 
plots and the 5-row plots. In some cases the former are more va- 
riable ; in others the latter ; and in no case is the difference in varia- 
bility great. These results are contrary to the general impression that 
variability decreases with increase in size of plots. Apparently, in 
tests of this kind, the 3-row plot is lai'^ge enough to give a fair sample 
and nothing is gained by adding the other two rows. When it is con- 
sidered that th.e addition of these two rows undoubtedly introduces 
systematic error from competition to a greater or less extent, and 
involves a very considerable increase in the labor of harvesting and 
threshing, there remains little doubt that the border rows of 5-row 
plots are best discarded in .experiments of this sort. 

Replication of Plots. — It is generally considered that the error 
from soil variability may be reduced to any desired point by replica- 
tion in sufficient degree. For any given degree of precision the num- 
ber of replications required is dependent on the variability of the 
replicate plots. When every plot in a single-row test is provided with 
two border rows the area required for the test is tripled, the replicate 
plots are separated more widely, and variability is usually increased, 
since the range of soil variability will usually be greater when a larger 
area is included. 

The removal of border effect from the rows harvested for yield 
may in some cases reduce variability more than enough to balance this 
increase, but when the unprotected single rows are grown in the same 
order in each series, variability will not be much affected by competi- 
tion, as before stated. Consequently more replications of single-row 



Expe;riments in Fiei^d Plot Te;chnic 



51 



plots protected by borders than of the single-row plots not so pro- 
tected may actually be required for a given degree of plot variability. 
Similarly, more replications may be required in a test of a large num- 
ber of strains than in a test of a small number, as Montgomery" has 
suggested. 

The number of replications required may be determined with a 
fair degree of accuracy from the variability of the check plots. The 
variability of the check plots in parts of the large fields used as com- 
pared with the variability of the check plots in the whole fields shows 
the importance of this point. In Table 25 are given the standard de- 

Table 25. — Relation of Plot Variability to Size of Experiment Field. 
Check Plots in Wheat Variety Test 1920. 





No. of 








Size of field 


Plots 


Yield 


Standard deviation 






bu. per acre 


bu. 


% 


Four ranges (1st)* 


20 


14.79 


3.789 


25.62 


Four ranges (2nd) 


20 


18.35 


4.073 


22.20 


Four ranges (3rd) 


20 


16.67 


3.659 


21.94 


Four ranges (4th) 


20 


20.74 


3.876 


18.69 


Mean 


20 


17.64 


3.849 


22.11 


Eight ranges (1st) 


40 


16.57 


4.316 


26.05 


Eight ranges (2nd) 


40 


18.71 


4.285 


22.90 


Mean 


40 


17.64 


4.302 


24.48 


Sixteen ranges 


80 


17.64 


4.430 


25.11 



*The four-range and eight-range sections are in order from west to east. 



viations of the yields of the check plots in the wheat variety test of 
1920. The yields of the three interior rows of the check plots were 
used in computing these constants. 

Twenty-four varieties could have been replicated four times in 
the four ranges comprising any quarter of the field. As the probable 
error of a single plot yield is 14.92 per cent we may conclude that the 
probable error of the mean of four such yields would be about 7.46 
per cent. But when 96 varieties must be tested, as they were in this 
test, four replications require 16 ranges, and the probable error of the 
mean yield becomes 8.47 per cent. A degree of precision which could 
be attained with four replications in a test covering four ranges could 
hardly be attained with five replications in a test covering sixteen 
ranges. 

Corresponding data for the wheat variety test of 1921 are given 
in Table 26. Although the variability in this experiment was much 
lower, the relative variability of large and small experiment fields was 



52 



Missouri Agr. Exp. Sta. Research Bulletin 49 



Table 26. — Relation of Plot Variability to Size of Experiment Field. 
Check Plots in Wheat Variety Test 1921. 



Size of field 



Four ranges (1st)* 
Four ranges (2nd) 
Four ranges (3rd) 
Rour ranges (4th) 

Mean 
Eight ranges (1st) 
Eight ranges (2nd) 

Mean 
Sixteen ranges 



No. of 
Plots 



Yield 
bu. per acre 



Standard Deviation 
bu. % 



16 

16 

16 

16 

16 

32^ 

33' 

32 

64 



15.78 
15.48 
15.28 
13.01 
14.89 
15.63 
14.14 
14.89 
14.89 



1.584 


10.04 


1.586 


10.25 


2.099 


13.74 


2.091 


16.07 


1.840 


12.53 


1.592 


10.19 


2.383 


16.85 


1.988 


13.52 


2.159 


14.50 



*The four-range and eight-range sections are in order from west to east. 



similar. Again the degree of accuracy obtained with four repHcations 
in four ranges would have been unattainable with five replications in 
16 ranges. 

The oats variety test and strain test in 1921 were contiguous, oc- 
cupying 24 ranges, with 120 check plots of Kherson oats, or one in 
every sixth plot. The variability of these check plots in sections of 

Table 27. — Relation of Plot Variability to Size of Experiment Field. 
Check Plots in Oats Variety and Strain Test, 1921. 





No. of 








Size of field 


plots 


Yield 


Standard deviation 






bu. per acre 


bu. 


% 


Four ranges (1st) 


20 


35.81 


4.75 


13.26 


Four ranges (2nd) 


20 


34.95 


2.90 


8.30 


Four ranges (3rd) 


20 


38,14 


4.21 


11.04 


Four ranges (4th) 


20 


39.60 


4.66 


11.77 


Four ranges (5th) 


20 


38.91 


4.14 


10.65 


Four ranges (6th) 


20 


40.31 


4.14 


10.27 


Mean 


^0 


37.95 


4.13 


10.88 


Eight ranges (1st) 


40 


35.38 


3.96 


11.19 


Eight ranges (2nd) 


40 


38.87 


4.50 


11.58 


Eight ranges (3rd) 


40 


39.60 


4.21 


10.62 


Mean 


40 


37.95 


4.22 


11.13 


Twelve ranges (1st) 


60 


36.30 


4.25 


11.71 


Twelve ranges (2nd) 


60 


39.60 


4.36 


11.01 


Mean 


60 


37.95 


4.31 


11.36 


Twenty-four ranges 


120 


37.95 


4.61 


12.15 



Experiments in Field Plot Technic 53 

four, eight, and twelve ranges, and in the whole field of 24 ranges, is 
shown in Table 27. 

The variability of the whole field of 24 ranges was 12 per cent 
greater than the average variability of sections of four ranges each. 
In this case again, five replications in the larger field would have given 
less accurate results than four replications in the smaller. 

In each of the cases cited above a steady increase in variability 
is apparent as the size of the experiment field is increased. It is obvious 
that the substitution of 3-row plots with discarded borders for single 
rows will result in greater variability, and will require increased rep- 
lication for the same degree of accuracy. 

From the foregoing statements it will be clear that the number of 
replications necessary for a given degree of accuracy may vary con- 
siderably with conditions. The number to be used in any specific ex- 
periment should be determined from the variability of the field in 
question and the degree of accuracy required. The variability of the 
check plots is usually considered a measure of the variability of the 
field. But when the number of replications to be used or the extent of 
experimental error is determined from the variability of the check 
plots, it is assumed that the variability of different varieties of the same 
crop is approximately the same under the same conditions. This of 
course is not strictly true. The yield of two varieties may be deter- 
mined by very different factors, as has been stated, and their relative 
variability may also be quite different. The variability of 120 plots 



Table 28. — Son, Heterogeneity of an Experiment Field as Determined From 

Yields of Two Check Varieties. 

Oats Variety and Strain Tests. 1931. 

Number Average Probable error of a 

Check variety of plots yield Standard deviation single yield determination 

bu. bu. % bu. % 

Kherson 120 37.95 4.61 13.15 3.11 8.30 

Red Rustproof 130 22.44 3.99 17.78 2.69 11.99 



each of Kherson and Red Rustproof oats, grown side by side as check 
plots in the oats variety and strain test of 1921, illustrate the possibil- 
ity of a serious error in the use of the standard deviation of check 
plots as a measure of the variability of an experiment field. These 
determinations are shown in Table 28. 

The field would have been considered decidedly less variable if 
Kherson had been used as the check variety than if Red Rustproof had 



54 Missouri Agr. Exp. Sta. Resi^arch Bulletin 49 

been used. Both of these are standard recommended varieties for the 
region, though they differ decidedly in their characteristics. Both 
have been used frequently as check varieties at the Missouri station in 
past seasons. From the variability of the Kherson check plots the mean 
yield of four replicate plots in this experiment would be considered 
to have a probable error of 4.10 per cent ; from the Red Rustproof plots 
the same determination would be given a probable error of 6.00 per 
cent. A degree of precision for which we would assume four replica- 
tions necessary, judging from the Kherson check, v/ould require nine 
replications according to the yields of the Red Rustproof check. 

The importance of choosing a check variety typical of the va- 
rieties tested, if its variability is to be considered a criterion of the 
variability of the field, is obvious. Whether it is possble to choose 
a "typical variety" for the purpose, in the case of ordinary variety 
tests, remains to be seen. 

ADJUSTMENT OF YIELDS BY MEANS OF CHECK PLOTS 

Adjustment of plot yields by the use of check plots has been a 
common practice in field experiments during recent years. It is 
recognized that no experiment field is perfectly uniform in produc- 
tivity, and the attempt is made, by means of the check plot adjustment, 
to compensate the varieties or treatments which chance to be located 
on the less productive plots for the resulting loss in yield. The com- 
mon method, in variety tests, is to distribute over the field, as fre- 
quently as practicable, check plots planted to the same variety and 
similarly handled in every way. The variation in yield among these 
check plots is then considered a measure of the productivity of the 
soil. By various methods, differing only in detail, the yields of the 
test plots in parts of the field giving high check yields are reduced, and 
those of test plots in parts giving low check yields are increased, in 
proportion to the productivity of the soil, as indicated by the yields 
of neighboring check plots. 

Previous Investigation. — Several investigations of the effect of 
such adjustment on the variability of replicate plots have been re- 
ported. The majority of these have been conducted in connection with 
experiments of the type discussed in the preceding section, in which 
uniformly handled fields have been harvested in small sections. Cer- 
tain of these sections, or plots, have been considered check plots, and 
on the basis of their yields the yields of the remaining plots have been 



EXPE^RIMENTS IN FlELD PlOT TeCHNIC 55 

adjusted. The reduction of variability of the adjusted plot yields is 
the measure of the efficiency of the method. 

Morgan" reports an experiment of this sort, in which 63 plots, 
planted first to wheat and then to fodder corn, in the same season, 
were used. The variability of the plot yields was steadily reduced as 
the number of check plots was increased. 

In a similar experiment reported by Lyon", in which Z7 replicate 
1/100 acre plots of corn were harvested, the use of checks in every 
second or third plot was found to reduce variability, but they were of 
little value when farther apart. 

Montgomery" states that alternating check plots with test plots 
gives a high degree of accuracy, but the total number of plots required 
when this method is used is greater than when the same degree of ac- 
curacy is attained by the use of replication. 

Kiesselbach" reports a comprehensive trial of three methods of 
adjusting yields by means of check plots in a uniform field of 207 
1/30-acre plots of Kherson oats. The effect on plot variability is shown 
in Table 29. 

Table 39. — Effect on Plot Variability op Adjusting Yields by Check 
Plots (Kiesselbach). 

Coefficient 
Method of of variability 

adjustment Actual Adjusted 

yields yields 

Alternate check plots. 
Correction based on 
average of two ad- 
jacent checks 7.85 7.01 

Checks every third plot. 

Correction based on one 

adjacent check plot 7.79 7.35 

Checks every third plot. 
Correction by progres- 
sive method, based on 
two nearest checks 7.87 6.57 



From these results Kiesselbach concludes "The yield of system- 
atically distributed check plats cannot be regarded as a reliable meas- 
ure for correcting and establishing correct theoretical or normal 
yields for the intervening plats." 

It should be noted at this point that even if adjustment by check 
yields were found invariably effective in experiments of this sort, 



56 Missouri Agr. Exp. Sta. Research Bulletin 49 

its value in ordinary variety testing would not be definitely estab- 
lished. The practice involves not only the assumption that the yields 
of the check plots are a fair indication of the productivity of the in- 
tervening plots for the check variety, but the further assumption that 
different varieties respond similarly to differing growing conditions. 
Adjustment of yields should therefore give better results in such ex- 
periments as those cited above than it could be expected to give in 
actual variety tests. 

This point is well illustrated by observations reported by Salmon". 
Two varieties of barley, Gatami and Odessa, were grown side by side 
in fiftieth-acre plots in five distributed portions of a field. Gatami gave 
an average yield of 18.3 bushels per acre, with quite uniform yields in 
the five plots, as evidenced by their probable error of 0.68 bushel, 
while Odessa yielded 13.3 bushels per acre in the first plot, 6.35 bushels 
per acre in the second, and a negligible yield in the other three. Ob- 
viously the adjustment of the yield of either of these varieties on the 
basis of the other variety as a check, would enormously increase 
rather than decrease the experimental error. As Salmon points out, 
an error similar in kind though less in degree may occur commonly 
in variety tests, when the yields of varieties are determined by dif- 
ferent limiting factors. And if this is generally the case, adjustment 
by check yields will be of doubtful value, even if it were found to 
eliminate variability completely in uniform plot tests. 

There is a growing tendency, consequently, to discontinue the use 
of check plots for adjusting yields in variety tests, and to use them 
only to measure soil variability and to indicate the degree of error 
in yield determinations of the tested varieties. Adjustment of yields 
has never been as common in preliminary tests as in tests on larger 
plots, principally because of the great amount of computation neces- 
sary in adjusting the yields of ten or twenty replicate rod-rows of a 
large number of varieties, and because the yield of a single rod-row, 
exposed to varying competition and materially affected by small me- 
chanical errors, is at best a very unreliable measure of productivity on 
which to base the adjustment of the yields of several other plots. 

Experimental Results. — It would of course be very desirable to 
use check plots for reducing plot variability, if the method could be 
relied on, because of the economy of the practice. The only certain 
method of reducing plot variability is by means of replication, and it 
may be considered a fairly general rule that the variability of plots 
on a given field, as measured by the standard deviation or the prob- 
able error, will in general be reduced by replication in proportion to 
the square root of the number of replications. In other words, the 



Experiments in Field Plot Technic 57 

variability of the mean of 16 replicate plots will be about half that of 
the mean of 4 replicate plots. Now the maximum use of check plots, 
that is, the practice of alternating check plots and test plots, requires 
the same land and labor as would be required by doubling the num- 
ber of replications, if no check plots were used. As doubling the 
number of replications will in general give a standard deviation about 
equal to the original standard deviation divided by the square root of 

2, it will reduce variability about 30 % | — = =.7071 | . If alternat- 

ing with check plots will consistently reduce variability more than 30 
per cent it will be generally a more economical way to control error. 
Similarly, the use of check plots in every third plot requires as much 
land as would be required by increasing the number of replications by 
50 per cent (using three replications instead of two, or fifteen instead 
of ten). From this relation the reduction of variability necessary if 
this practice is to equal replication in effectiveness can be easily com- 
puted. Such determinations for check plots at various intervals are 
shown in Table 30. 

Table 30. — Reduction of Variability by the Use of Check Plots Equivalent 

TO That Probably Attainable With the Same Number 

OF Plots by Replication. 











Reduction in 








standard deviation to 


Distribution of 


Equivalent increase in 


be 


expected by such 


check plots 


number 


of replications 


increase in replication 






% 




% 


Alternate plots 




100.00 




29.29 


Every third plot 




50.00 




18.35 


Every fourth plot 




33.33 




13.50 


Every fifth plot 




25.00 




10.55 


Every sixth plot 




20.00 




8.71 


Every seventh plot 




16.67 




7.41 


Every eighth plot 




14.29 




6.47 


Every ninth plot 




12.50 




5.75 


Every tenth plot 




11.11 




5.12 



If protected single-row or 3-row plots are used in preliminary 
experiments a more reliable measure of soil productivity is available, 
and consequently the adjustment of yields is more likely to be of value, 
than when unprotected single-row plots are used. By the use of 
planting plans of the sort employed in these experiments, it is pos- 



58 Missouri Agr. Exp. Sta. Research Bulletin 49 

sible to adjust the yields by a somewhat shortened method. If adjust- 
ment of yield is effective in reducing plot variability in this sort of 
test it can be accomplished with but little increase in labor. In each 
of the tests reported in this paper a trial of the effectiveness of adjust- 
ing yields by means of check plots was made, the criterion of accuracy 
being in each case the variability of the yields of the replicate plots of 
each variety. Since the number of replicate plots was only three 
or four the average deviation was determined instead of the stand- 
ard deviation. 

Method Used in Adjusting Yields. — The method employed in ad- 
justing yields may be described as follows: The average yield of all 
check plots and the relative yield of each check plot in terms of this 
average (that is, the quotient obtained by dividing the yield of the in- 
dividual check plot by the average yield of all check plots) were de- 
termined. The relative yield of each check plot, expressed in per- 
centage of the mean check yield, is designated hereafter as the "plot 
value" of that check plot. When the average yield of all check plots 
is 25 bushels per acre, the plot value of a check plot yielding 30 bushels 
per acre is 120 per cent — in other words it is 20 per cent more pro- 
ductive than the average. Now assuming gradual change in the pro- 
ductivity of the soil between check plots, each test plot is assigned a 
plot value by interpolation. The adjusted yield of each plot is then 
determined by dividing the actual yield by the plot value. 

The short method for adjusting yields, referred to above, is 
based on the fact that the varieties occur in the same order in each 
series. Thus in the field diagrammed in figure 1, the following se- 
quence of plots occurs in each of the four series : 

ck 1 17 33 49 65 81 ck 

Now if the average yield of the four check plots adjoining variety 
1, and the average yield of the four check plots adjoining variety 81 
are each given a plot value, corresponding plot values for the mean 
yields of varieties 1, 17, 33, 49, 65, and 81 may be interpolated, and 
the mean yields may be adjusted in one operation. The same method 
may be used, of course, regardless of the number of replications. The 
result will not be exactly the same as that of averaging the adjusted 
yields determined individually, but will in most cases approximate it 
closely, the slight dift'erence being caused by the disproportion of yield 
and plot value in the plots averaged. It is doubtful that either meth- 
od is consistently more accurate than the other. 

When the check plot yield is used in the adjustment of the yields 
of other plots it is of course essential that it should be a reliable de- 
termination, not unduly affected by factors not affecting the neighbor- 



Experiments in Field Plot Technic 



59 



ing plots. For example if the yield of a check plot is reduced 20 per 
cent by a poor stand, the adjusted yields of neighboring plots will be 
increased to the same extent as if the check plot yield had been low be- 
cause of poor soil, and will consequently be considerably higher than 
they should be. It is important therefore that conditions be made as fa- 
vorable as possible for accurate yield testing when this method is used. 
One cause for poor results in the adjustment of yield in some of the 
experiments reported in this paper was failure to protect the outside 
strip of check plots by means of border rows, in a few of the tests, be- 



Tabi,e 31. — Relative Variability of Actual and Adjusted Yields. 
Average Deviation in Percentage of Yield. — Barley Variety Test 1919. 









Average 


deviation 




Planting 




Actual yields 


Adjusted yields 


number 


Variety 3 interior rovers 


5 rows 3 


interior rows 


5 rows 






% 


% 


% 


% 


1 


Hanna 906 


19.81 


17.82 


13.15 


10.80 


3 


Steigum 907 


15.17 


18.79 


13.48 


8.40 


3 


Luth 908 


29.97 


28.17 


5.51 


4.62 


4 


Eagle 913 


26.14 


29.79 


9.71 


12.98 


6 


Servian 915 


18.37 


17.97 


7.36 


5.59 


7 


Odessa 916 


2.31 


4.33 


23.99 


17.01 


8 


Lion 923 


14.65 


12.10 


11.37 


11.03 


10 


Horn 926 


4.08 


2.00 


16.45 


12.74 


11 


Odessa 927 


13.62 


9.16 


21.62 


13.76 


13 


Summit 929 


5.28 


6.45 


14.23 


11.59 


13 


Mariout 932 


11.02 


11.57 


18.68 


14.31 


14 


Odessa 934 


13.73 


13.91 


11.18 


10.31 


15 


Peruvian 935 


13.25 


17.87 


12.42 


16.82 


16 


Trebi 936 


11.27 


12.53 


18.78 


18.28 


18 


Oderbrucker 940 


10.77 


14.46 


13.60 


15.98 


19 


Prankish 953 


20.53 


19.65 


22.63 


18.49 


20 


Manchuria 956 


6.88 


6.33 


13.89 


10.68 


21 


Oderbrucker 957 


17.88 


13.62 


1.97 


3.37 


22 


Manchuria x Champion 39.47 


39.19 


21.93 


20.35 




of Vermont 










33 


Luth 972 


16.77 


18.61 


7.05 


7.48 


24 


Red River 973 


13.94 


11.02 


12.37 


12.33 


25 


Featherston 1118 


21.40 


20.89 


8.47 


13.39 


26 


Featherston 1119 


16.59 


15.25 


4.78 


12.26 


27 


Featherston 1120 


15.91 


13.64 


2.48 


6.44 


28 


Hanna x Champion 
of Vermont 1121 


16.00 


16.81 


28.36 


28.50 


29 


Manchuria 1125 


6.79 


14.42 


7.78 


1.55 


30 


Malting 1129 


12.86 


10.40 


5.40 


9.02 




Mean 


15.35 


15.44 


12.91 


12.15 



60 



Missouri Agr. Exp. Sta. Research Bulletin 49 



cause of lack of space. The check plots growing on the border of the 
field were materially reduced in yield, in some cases, notably the oats 
strain test of 1919 and the wheat variety test of 1921. In these cases 
the variability of the actual and adjusted yields has been computed 
both for all series and for the remaining series when the one affected 
by an unreliable check is discarded. 

Relative Variability of Actual and Adjusted Yields. — The relative 
variability of actual and adjusted yields of both 3-row and 5-row plots 
in the barley variety test is shown in Table 31. In this test there were 
three replications, and the check variety was Oderbrucker, in every 



Tab 


i,E 32.— Relative Variability 


OF Actual and Adjusted Yields. 




Average Deviation in 


Percentage of Yield 








Oats Variety Test 1919. 












Average Deviation 




Planting 




3 Series 


4 : 


Series 


number 


Variety 


(3 interior rows) 


(3 interior rows) 






Actual 


Adjusted 


Actual 


Adjusted 






yields 


yields 


yields 


yields 






% 


% 


% 


% 


1 


A. sterilis nigra 


4.32 


1.46 


9.18 


5.02 


2 


Black Mesdag 


9.03 


9.69 


7.29 


12.90 


3 


C. I. 602 


13.72 


16.00 


16.30 


13.63 


3 


C. I. 603 


4.72 


3.09 


5.84 


3.88 


5 


C. I. 620 


4.73 


10.14 


11.24 


13.67 


6 


Early Champion 


18.63 


15.18 


14.97 


14.65 


7 


Early Gothland 


14.20 


4.67 


11.55 


4.18 


8 


Garton 473 


5.99 


6.25 


8.42 


9.42 


9 


Garton 585 


14.08 


19.44 


16.92 


19.95 


10 


Golden Giant 


9.44 


14.31 


14.40 


15.09 


11 


Irish Victor 


9.69 


3.29 


7.72 


16.40 


12 


Japanese Selection 


6.87 


4.71 


11.85 


5.20 


13 


June 


18.37 


11.19 


17.53 


10.37 


14 


Kherson Selection 


17.01 


9.20 


15.06 


20.36 


15 


Fulghum 


9.69 


11.36 


13.06 


17.32 


16 


Lincoln 


21.07 


12.54 


16.56 


11.83 


17 


Monarch 


6.12 


4.55 


9.06 


33.36 


18 


North Finnish 


8.69 


5.17 


7.84 


27.03 


19 


Scottish Chief 


5.05 


4.28 


5.10 


15.42 


20 


Sparrow bill (Missouri) 


10.98 


10.82 


12.38 


13.15 


21 


Sparrow bill (Cornell) 


4.45 


3.25 


12.11 


3.85 


22 


Tobolsk 1 


6.17 


3.85 


13.92 


5.38 


23 


Tobolsk 2 


11.56 


9.24 


20.35 


13.96 


24 


White Tartar 


10.94 


4.75 


9.51 


4.54 




Mean 


10.23 


8.27 


12.01 


12.94 



Experiments in Field Plot Technic 



61 



sixth plot. As a result of the adjustment of yields, the average devia- 
tion of 3-row plots was reduced from 15.35 per cent to 12.91 per cent, 
a reduction of 16 per cent, and that of 5-row plots from 15.44 per 
cent to 12.15 per cent, a reduction of 21 per cent. 

The relative variability of actual and adjusted yields in the oats 
variety test of 1919 is shown in Table 32. In this field the check. 
Red Rustproof, was in every ninth plot. When the series affected by 
the faulty check yields of the border plots is included the variability of 
the adjusted yields is slightly higher than that of the actual yields, 
but when this series is discarded the average variability as measured 
by the mean deviation is reduced 19 per cent. 

It might be expected that the oats strains grown on the same field 
would show a greater reduction of variability than the varieties, since 
practically all of them were of the same variety as the check, and since 

Table 33. — Relative Variability of Actual and Adjusted Yields. 

Average Deviation in Percentage of Yield. 

Oats Strains Test 1919. 



Planting Accession 
number number 



Average deviation 
Actual yields Adjusted yields 

interior rowrs 5 rows 3 interior rows 5 rows 
% % % % 



1 


0119 


10.30 


7.75 


11.23 


8.81 


2 


0120 


4.70 


6.58 


3.01 


1.76 


3 


0121* 


5.76 


3.25 


4.57 


4.14 


4 


0122 


4.62 


3.52 


6.46 


3.82 


5 


0123 


9.91 


8.25 


11.47 


9.62 


6 


0125 


3.18 


3.34 


5.39 


6.60 


7 


0126 


7.62 


5.95 


10.56 


16.58 


8 


0127* 


6.76 


5.09 


6.92 


9.85 


9 


0124* 


6.13 


6.34 


4.92 


4.59 


10 


0133 


7.07 


4.77 


3.92 


5.36 


11 


0128 


4.17 


3.56 


3.58 


3.36 


12 


0129 


5.03 


7.07 


5.94 


6.35 


13 


0130 


4.20 


2.62 


6.74 


9.72 


14 


0131 


3.59 


2.59 


4.98 


2.94 


15 


0132 


7.38 


5.81 


12.38 


12.08 




Mean 


5.96 


5.10 


6.80 


7.04 



* Not taxonomically Red Rustproof. 



the check plots were more frequent, being in every sixth plot. The 
results of adjusting yields in this test, both for protected 3-row plots 
and for unprotected 5-row plots in four series are shown in Table 33. 
Contrary to expectation, the variability was not reduced by adjustment 



62 



Missouri Agr. Exp. Sta. Research Bulletin 49 



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Experime;nts in Field Plot Tlchnic 63 

of yield. A possible explanation is the extremely low variability of the 
actual yields, indicating that the field, which was quite small, was re- 
latively uniform. Any gain in uniformity from a check adjustment 
of yields would of course be expected to be greater in highly variable 
than in more uniform fields. The relative uniformity of this field 
is indicated not only by the low mean deviation of the test plots, but 
also by the low standard deviation of the check plots, which was only 
11.68 per cent, as compared with a standard deviation of 22.59 per 
cent in the check plots of the adjoining oats variety test. 

The effect of adjusting yields on the variability of 3-row and 
5-row plots in the wheat variety test of 1920 is shown in Table 34. 
In this test the check variety, Fultz, was grown in every seventh plot. 
There were four series of the ninety-six varieties. 

The reduction in variability was very marked, being 37 per cent 
for 3-row plots and 42 per cent for 5-row plots. The variability of 
almost every variety was reduced, and the reliability of the results 
was undoubtedly much increased. 

The wheat variety test of 1921, occupying an equal area on a 
neighboring field, and with similar varieties and the same planting 
plan, gave decidedly different results. In this field the check va- 
riety was Poole. Several check plots on the border were abnormal, 
and the computations are therefore given both for three series and for 
four, the series affected by the abnormal check yields being dis- 
carded in the former case. The relative variability of actual and ad- 
justed yields is shown in Table 35. 

Although the check yields are somewhat less variable for three 
series than for four, the adjustment was not effective in either case in 
reducing variability. The adjusted yields are 10 per cent more va- 
riable than the actual yields for the three series and 34 per cent higher 
for the four. 

Similar results were obtained in the wheat mixture test of the 
same season, in which several of the same varieties were included, 
and the same check variety was used. In this test the check variety 
was in every sixth plot, and four replications were used. The results 
of adjusting yields are shown in Table 36. Variability was increased 
from 9.84 per cent to 13.81 per cent, an increase of 40 per cent. Thus 
the results of adjusting yields of wheat varieties in 1921 are directly 
contrary to the results of the same practice in 1920. 

Difference in Results Obtained by Adjustment with Different 
Check Varieties. — In the oats variety and strain tests of 1921, two 
check varieties, Kherson and Red Rustproof, were grown. In these 
tests 96 strains were included, 32 of Kherson, 32 of Red Rustproof, and 



64 



Missouri Agr. Exp. Sta. Rkse;arch Bulletin 49 



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Experiments in Field Plot Technic 



65 



Table. 36— Relative Variability of Actual and Adjusted Yields. 
Average Deviation in Percentage of Yield. Wheat Mixture Test 1921 









Average 


Deviation 


Planting 






Actual yields 


Adjusted yields 


number 


Variety 




(3 interior 
rows) 


(3 interior 
rows) 


1 


Fulcaster 




9.67 


16.90 


2 


Harvest Queen 




9.35 


21.47 


3 


Mixture No. 1 




6.12 


20.11 


4 


Michigan Wonder 




7.88 


20.51 


5 


Nigger 




2.33 


20.16 


6 


Michigan Wonder No. 


31 


4.93 


13.86 


7 


Michigan Wonder No. 


54 


12.96 


16.03 


8 


Mixture No. 2 




15.38 


17.86 


9 


Michigan Wonder No. 


96 


4.99 


13.88 


10 


Michigan Wonder No. 


209 


5.30 


14.83 


11 


Beechwood Hybrid No. 


12 


9.04 


11.01 


13 


Beechwood Hybrid No, 


. 85 


14.98 


15.49 


13 


Mixture No. 3. 




16.76 


10.47 


14 


Beechwood Hybrid No 


. 87 


10.16 


11.94 


15 


Beechwood Hybrid No. 


207 


20.80 


11.81 


16 


Michigan Wonder No. 


221 


7.13 


8.90 


17 


Kanred 




10.09 


12.86 


18 


Mixture No. 4 




10.39 


8.44 


19 


New York 123-32 




16.73 


12.09 


20 


Red Rock 




14.04 


10.68 


21 


Red Hussar 




12.71 


17.42 


22 


Turkey (Kansas) 




17.32 


13.74 


23 


Mixture No. 5 




2.87 


12.73 


24 


Michigan Amber 




3.39 


10.71 


25 


Nigger 




4.09 


10.47 


26 


Fulcaster (Co-op) 




2.09 


14.25 


27 


Fulcaster (Outl) 




11.97 


17.18 


28 


Mixture No. 6 




11.19 


7.75 


29 


Fulcaster (Blazier) 




11.41 


6.77 


30 


Fulcaster (Cowles) 




9.09 


14.11 




Mean 




9.84 


13.81 



32 of other varieties. The yields were adjusted by means of each 
check variety separately, to determine the relation between the ef- 
fectiveness of yield adjustment and the similarity of the check to the 
tested variety. The results of this adjustment on plot variability are 
shown in Tables VI and 38. 

The variability of the yields of the Red Rustproof strains was 
somewhat reduced (6 per cent) by adjustment according to the yields 



66 



Missouri Agr. Exp. Sta. Research Bulletin 49 



Tabli; 37. — Relative Variability of Actual and Adjusted Yields. 
Average Deviation in Percentage of Yield. Oats Variety Test 1931 







Average deviation 




Planting 




Actual yields 


Adjusted yields 


number 


Variety 


(3 interior 


(3 interior 


rows) 






rows) 


(Kherson) (Red Rustproof) 






% 


% 


% 


65 


Burt 


10.23 


11.54 


11.00 


66 


Canadian 


9.29 


8.93 


18.37 


67 


C. I. 603 


9.21 


4.94 


13.89 


68 


Culberson 


6.46 


8.80 


4.44 


69 


Danish Island 


10.53 


8.83 


12.56 


70 


Early Dakota 


9.33 


7.96 


11.45 


71 


Early Gothland 


10.00 


19.16 


14.69 


72 


Carton 748 


14.35 


13.36 


14.77 


73 


Green Russian 


9.75 


11.23 


13.75 


74 


Irish Victor 


9.43 


8.07 


15.99 


75 


Joanette 


30.75 


29.36 


26.94 


76 


Fulghum 043 


5.19 


8.50 


8.99 


77 


Monarch 


4.76 


6.36 


8.54 


78 


Monarch Selection 


2.89 


5.74 


11.55 


79 


Scottish Chief 


10.95 


15.01 


8.66 


80 


Silvermine 050 


11.24 


9.88 


9.21 


81 


Silvermine Selection 


11.25 


16.14 


3.16 


83 


Sparrowbill (C) 


23.93 


23.03 


25.23 


83 


Sterilis Selection 


8.02 


7.30 


9.17 


84 


Storm King 


11.68 


13.94 


13.15 


85 


Swedish Select 057 


14.48 


14.89 


11.80 


86 


Fulghum 065 


8.81 


11.04 


9.41 


87 


Fulghum 0113 


22.19 


11.18 


15.85 


88 


Silvermine 0115 


8.38 


6.29 


3.59 


89 


Silvermine 0117 


6.90 


8.95 


9.69 


90 


Fulghum 0124 


5.17 


3.38 


7.89 


91 


Fulghum 0145 


9.81 


8.63 


15.66 


92 


Fulghum 0149 


10.19 


10.77 


15.70 


93 


Fulghum 0151 


10.85 


13.71 


10.80 


94 


Fulghum 0153 


9.07 


14.59 


19.61 


95 


Silvermine 0165 


5.63 


11.33 


4.62 


96 


Swedish Select 0165 


16.74 


14.03 


8.74 




Mean 


10.86 


11.43 


12.15 



of the Red Rustproof check, but was slightly increased (2 per cent) 
when the Kherson check was used. On the other hand, the variability 
of the yields of the Kherson strains, though not reduced by either check, 
was increased only 4 per cent by the Kherson check, while it was in- 
creased 48 per cent by the Red Rustproof check. Neither check was 
effective in adjusting the yields of the other varieties, the Kherson 



Experiments in Field Plot Technic 



67 



Table 38. — Relative Variability of Actual and Adjusted Yields. 
Average Deviation in Percentage of Yield. — Oats Strain Test 1921 
(Red Rustproof and Kherson) 





Red 


Rustproof 


strains 




Kherson strains 






Average deviation 






Average deviat 


on 


u 
v 

E 

3 


Strain 


3.2 

^1 


Adjusted 
(3 interior 


yields 
rows) 


V 

e 

3 
bo 


Strain 


a ; 

3 2 
" ^> 


Adjusted yields 
(3 interior rows) 




(Kher- 
son) . . 


(Red 
Rust- 
proof) 


(Kher- 
son) . . 


(Red 

Rust- 
proof) 






% 


% 


% 






% 


% 


% 


1 


066 


18.13 


15.48 


13,04 


2 


023 


15.80 


7.59 


12.93 


3 


067 


12.89 


14.19 


11.36 


4 


040 


3.86 


5.59 


10.45 


5 


068 


23.14 


21.34 


12.47 


6 


041 


9.50 


5.82 


4.07 


7 


069 


21.55 


20.54 


11.70 


8 


052 


3.46 


2.83 


10.49 


9 


072 


14.29 


12.26 


10.34 


10 


053 


6.26 


5.97 


10.14 


11 


074 


12.18 


17.23 


13.94 


12 


079 


11.49 


9.91 


10.20 


13 


075 


13.40 


18.28 


18.80 


14 


080 


1.72 


7.02 


13.20 


15 


0118 


28.77 


32.06 


26.92 


16 


082 


6.19 


8.74 


15.01 


IS 


0119 


10.32 


13.47 


13.62 


17 


083 


5.31 


5.88 


9.26 


20 


0120 


7.28 


6.11 


12.32 


19 


085 


8.69 


10.65 


7.30 


22 


0122 


17.16 


12.32 


14.20 


21 


086 


11.73 


7.45 


8.45 


24 


0125 


10.91 


11.52 


8.40 


23 


fixture** 


• 4.87 


3.84 


9.19 


26 


0126 


10.41 


10.24 


4.66 


25 


088** 


13.04 


13.79 


9.16 


28 


0128 


14.48 


17.36 


2.76 


27 


089 


4.69 


6.77 


12.89 


30 


0129 


7.89 


6.31 


7.44 


29 


090 


2.84 


4.85 


10.64 


32 


0130 


7.99 


11.78 


9.17 


31 


091 


12.46 


14.67 


10.84 


33 


0131 


12.43 


13.96 


13.23 


34 


094 


4.59 


6.43 


6.57 


35 


0132 


17.77 


14.67 


12.11 


36 


095 


4.36 


4.96 


14.62 


37 


0133 


14.07 


11.63 


13.55 


38 


096 


4.39 


7.71 


4.66 


39 


0134 


29.91 


30.37 


29.50 


40 


097 


5.53 


6.97 


11.80 


41 


0135 


14.36 


17.58 


13.11 


42 


098 


9.09 


10.03 


13.18 


43 


0136* 


7.80 


7.59 


12.69 


44 


099 


6.89 


6.26 


10.20 


45 


0141 


12.58 


13.30 


11.11 


46 


0100 


6.90 


4.65 


8.55 


47 


0163 


2.70 


1.82 


14.28 


48 


0155 


12.75 


4.49 


23.56 


50 


0169 


21.95 


17.79 


23.03 


49 


0157 


6.34 


7.40 


14.18 


52 


0181 


9.95 


7.62 


9.69 


51 


0158 


10.81 


12.24 


6.26 


54 


0182 


26.12 


21.76 


20.84 


53 


0159 


6.33 


10.82 


8.26 


56 


0183* 


4.52 


5.51 


8.99 


55 


0160 


4.98 


6.12 


12.52 


58 


0383 


10.10 


15.60 


20.18 


57 


0161 


5.55 


9.19 


9.27 


60 


0391 


9.55 


11,37 


6.47 


59 


0162 


11.28 


13.38 


9.47 


62 


0394 


13.03 


11.52 


10.29 


61 


0167 


2.65 


3.37 


4.41 


64 


0395 


8.69 


11.40 


17.96 


63 


0174 


10.74 


8.96 


15.67 


W 


ean 


14.47 


14.70 


13.55 


Mean 


7.16 


7.44 


10.59 



• Not taxonomically Red Rustproof. Excluded from average. 
** Not taxonomically Kherson. Excluded from average. 
♦••Mixture of strains 082, 094, 0100, 0174. 

check increasing their variability 7 per cent, and the Red Rustproof 
check 20 per cent. These results indicate the importance of using 
a check variety typical of the varieties tested, when adjustment of 
yields is to be made ; and the danger of increasing rather than decreas- 



68 



Missouri Agr. Exp. Sta. Research Bulletin 49 



ing error by this practice when the tested varieties are quite different 
in habit from the check variety. 

The use of an unsuitable check variety not only increases the 
margin of error, but it may cause very deceptive comparative results. 
For example, the average yields of the Kherson strains 0155 and 0157, 
unadjusted and adjusted according to the yields of both check va- 
rieties, are shown below : 





Strain 


Method 


0155 


0157 




Yield 


Average 
Deviation 


Yield 


Average 
Deviation 


Unadjusted 

Adjusted by Kherson check 

Adjusted by Red Rustproof check 


37.50 
34.50 
39.94 


12.75 

4.49 

23.56 


43.69 
43.69 
39.38 


6.34 

7.40 

14.18 



The 17 per cent advantage in yield of strain 0157 is increased to 
27 per cent by the Kherson adjustment, and since the variability of 
the replicate yields is reduced by the adjustment we may fairly as- 
sume that the latter is the more reliable figure. But when the Red 
Rustproof check is used for adjusting yields, the advantage of strain 
0157 disappears entirely. The inaccuracy of the yields adjusted by 
Red Rustproof is indicated by the increase in plot variability result- 
ing from this adjustment. Thus the adjustment of yields by means 
of check plots may mask considerable differences in yields between the 
varieties under test. 

Although Kherson and Red Rustproof are decidedly different in 
type, both are commonly grown in Missouri, and both have been used 
frequently here as check varieties in oats variety tests. It is interesting 



Tabi:,e 39. — Relative Variability of Actual and Adjusted Yields of Kherson 

AND Red Rustproof Oats, Each in 120 Distributed Plots. 

Oats Variety and Strain Tests 1921. 



Variety 

Kherson 

Red Rustproof 



Yield 
Actual Adjusted 


Standard deviation 
Actual Adjusted 
yield yield 
% % 


37.95 39.04 


12.15 


20.79 


22.44 22.80 


17.78 


19.92 



Experiments in Field Plot Technic 



69 



to determine the effect on variability of adjusting the yields of the 
120 plots of Kherson, on the basis of those of the 120 plots of Red 
Rustproof adjoining them, and those of the 120 plots of Red Rustproof, 
on the basis of the yields of the adjoining Kherson plots. In this 
adjustment the yield of each plot is divided by the plot value of the 
adjoining plot, and the method corresponds to method II used by 
Kiesselbach in the experiment cited above (see Table 29). The results 
of the yield adjustment are shown in Table 39. 

The adjustment of plot yields by means of check plots of a va- 
riety distinctly different in type resulted in a decided increase in plot 
variabihty, even though the plot values used were determined in each 
case by the yield of the immediately adjacent plot. If the yields 
of the Kherson and the Red Rustproof plots had been perfectly ac- 
curate measures of the productivity of the soil, the plot values of the 
adjacent plots would have been almost the same in each of the 120 
locations, and the adjustment of the yields of either variety by those 
of the other would have reduced variability almost to zero. Instead, 
variability was actually and very decidedly increased, because the sec- 
tions of the field which gave relatively high yields of Kherson, gave 
relatively low yields of Red Rustproof, and vice versa, in many cases. 
In fact, there was very little relation between the productivity of a 
portion of the field as determined by a Kherson check, and the pro- 



60 to 70 

70 to 80 

80 to 90 

90 to 100 

100 to 110 

110 to 120 

120 to 130 

130 to 140 

140 to 150 

150 to lee 

160 to 170 

170 to 180 
Total 



iH 


tH 


1-1 


iH 


l-H 


■-1 


iH 


w 


N 


N 


N 


(M 


W 


(M <M 
















1 
















1 




1 

1 


2 


4 


1 


1 


1 

1 
1 


1 
1 


1 


1 


1 






1 


2 




2 


2 


4 


3 


2 


3 


1 












1 




1 


4 


3 


2 


2 


2 


2 


1 










1 




3 


4 


1 


4 


4 


2 


3 








1 










5 


1 


2 


3 


3 


1 


1 


1 


1 










1 


1 


1 


3 
2 


2 
2 


2 


1 
















1 






2 


1 


1 
1 








1 



10 20 11 20 19 16 







1 

3 

6 
10 
20 
18 
22 
19 
11 

4 

5 

1 

120 



Figure 7. — Correlation Between Yields of Kherson Check Plots and 

Yields op Adjacent Red Rustproof Check Plots, in Oats Variety and 
Strain Tests 1921. 

rr= +.102 ± .060. 



70 



Missouri Agr. Exp. Sta. Research Bulletin 49 



ductivity of the same portion of the field as determined by an adjacent 
Red Rustproof check plot. This correlation is shown in figure 7. The 
coefficient of correlation is less than three times its probable error — 
the correlation has not even statistical significance ! The relative pro- 
ductivity of different portions of the field, as indicated by the two check 
varieties, is shown in figure 8. If Kherson had been used as a check 





Figure 8. — Relative Variabieity of Dieeerent Parts of an Experiment 
FiEED, as indicated by the Yields of Adjacent Check Plots of Kherson 
and Red Rustproof Oats. Oats Variety and Strain Tests 1921. In the 
diagram on the left, points of equal productivity, as indicated by the yields 
of the Kherson check plots, are connected by lines (as points of equal elevation 
are connected by lines on a contour map). In the diagram on the right, the 
same field is similarly mapped according to the yields of the Red Rustproof 
check plots. The numbers indicate the plot values of the points concerned. 

variety for adjusting yields, the yields of certain plots would have been 
increased to compensate for the low productivity of the soil ; if Red 
Rustproof had been used the yields of the same plots would have 
been decreased to compensate for the high productivity of the same 
soil. The fact is that certain parts of the field were actually more 
productive than the average for Kherson oats and less productive for 
Red Rustproof, as is indicated by the fact that each variety of check 
was considerably more effective in the adjustment of the yields of 
strains of the same variety than of strains of the other. But neither 
check was a very accurate measure of the productivity of the soil, 
even for its own variety, as indicated by the failure of adjustment to 
reduce variability consistently even when Kherson strains were ad- 



Expe;rime;nts in Field Plot Technic 



71 



justed according to the Kherson check and Red Rustproof strains 
according to the Red Rustproof check. 

Value and Limitations of Adjusting Yields by Meaxns of Check 
Plots. — The effect on plots variabiUty of adjusting yields by means of 
check plots in all of the tests is shown in summary form in Table 40. 
The variability of the test plots was reduced by adjustment in three 
tests and was increased in the other five. It is noteworthy that the 
three tests in which plot variability was reduced by adjustment were 
characterized by high plot variability, as indicated by the standard 
deviation of check plots, while the tests in which adjustment was not 

Table 40. — Summary of Relative Variability of Actual and Adjusted 
Yields of Interior Rows in All Tests. 







Number 


Number 


Average 


deviation 


Test 


Season 


of var- 


or rep- 


Actual 


Adjusted 






eties or 


lica- 


yields 


yields 






strains 


tions 


% 


% 


Barley Variety 


1919 


27 


3 


15.35 


12.91 


Oats Variety 


1919 


24 


3 


10.23 


8.27 


Oats Strain 


1919 


15 


4 


5.96 


6.80 


Wheat Variety 


19'20 


94 


4 


24.27 


15.32 


Wheat Variety 


1921 


94 


3 


10.45 


11.52 


Wheat Mixture 


1921 


30 


4 


9.84 


13.81 


Oats Variety 


1921 


32 


4 


10.86 


11.43* 


Oats Strain 


1921 


64 


4 


10.82 


11.07* 



* Adjustment by Kherson check. 

effective were in general low in plot variability. In 1919 adjustment 
was quite effective in reducing variability in the oats variety test, while 
it increased variabiHty in the oats strain test, which was conducted on 
the same field and similarly handled in every way. In fact, conditions 
were considered more favorable for the effectiveness of the practice 
in the strain test than in the variety test, for the check plots were closer 
together and 12 of the 15 strains tested were taxonomically identical 
with the check. But the standard deviation of check plots on the 
part of the field on which varieties were grown was almost twice as 
great as on the part of the field on which the strains were grown. Ap- 
parently the high variability of the plots in the variety test was caused 
in large part by differences in actual soil productivity which were 
largely counteracted by the adjustment of yields, while there was 
little variation in soil productivity in the strain test and such plot 
variability as occurred was largely due to other factors. In general 
therefore the adjustment of yields will probably be found more ef- 



72 Missouri Agr. Exp. Sta. Research Bulletin 49 

fective on fields highly variable in soil productivity than on more 
uniform fields, and for similar reasons the method will probably be 
found more effective in tests covering a rather large area than in tests 
covering a smaller area. 

It is clear that the adjustment of yields by means of check plots 
entails several serious disadvantages, and may increase experimental 
error considerably. Not only is the yield of the check plot a far from 
perfect measure of soil productivity for the check variety, but the pro- 
ductivity of the same soil for other varieties may be decidedly dif- 
ferent. The method is therefore more effective in tests of strains of 
the same variety as the check, than in tests of different varieties. When 
the yields of check plots are materially affected by factors not similarly 
affecting the neighboring test plots, adjustment of yields will increase 
experimental error. The check plots must therefore be effectively 
protected from competition, border effect, mechanical errors, and the 
like. Moreover, it is to be expected that the effectiveness of adjusting 
yields will vary with the season, since the relative influence of soil 
productivity on yield varies with the season. For example, in a season 
in which winter injury is exceptionally severe, actual soil fertility may 
have comparatively little to do with plot yields. Now, if the check 
variety is hardy, its yields may vary with the soil fertility, but when 
corresponding adjustments are made on the yields of tested varieties 
limited in yield by winter injury, a decrease in the variability of repli- 
cate plots is hardly to be expected. The same considerations apply 
of course to yields limited by many other factors. 

But, although a multitude of objections may be made to the 
theoretical bases of the practice of adjusting yields in variety tests, 
and although in many cases it undoubtedly results in an increase rather 
than a decrease in experimental error, the practice offers promise of 
value and is worthy of further investigation. The effectiveness of 
the adjustment of yields in the wheat variety test of 1920, in which 
the variability of replicate test plots was reduced about 40 per cent, 
is a demonstration of the possibilities of the method. An increase in 
replication of plots involving the same increase in land and labor would 
probably have reduced plot variability only about 7 per cent. A thor- 
ough knowledge of the value and limitations of yield-adjustment by 
means of check plots might enable us to reduce variability, at least in 
some types of plot tests, much more effectively by this means than 
by replication. The saving in area required is of particular significance 
in preliminary tests if border rows must be used for the elimination 
of competition, since in this case the area required for a large number 
of replications is in many cases prohibitive. 



Experiments in Field Plot Technic 73 



CONCLUDING REMARKS 

The best method for preliminary variety testing is one which will 
permit the accurate determination of the relative value of the va- 
rieties under field conditions, with the use of a small area of land for 
each variety. Some precision must be sacrificed to save land, and in 
so far as the errors involved are of such nature that their extent can 
be approximately determined, and conclusions drawn accordingly, this 
sacrifice of precision is permissible. In many cases it is advisable, for 
example, to reduce the number of replications and to increase the least 
difference in yield regarded significant to a sufficient degree to com- 
pensate for the decrease in precision. 

But these considerations do not apply to systematic errors, which, 
since they affect the yields of replicate plots similarly, and consequently 
have little effect on plot variability, cannot be accurately measured. 
Typical systematic errors commonly involved in preliminary testing 
are (1) modification of growing conditions favoring some varieties 
more than others, such as hand planting or wide spacing between rows, 
and (2) competition between varieties of different type, resulting from 
the use of single-row plots. The relative value of varieties under 
such conditions may be vastly different from their relative value un- 
der typical field conditions. Even should measurable experimental 
error be reduced to the absolute minimum, such a variety test might 
give results entirely misleading. The error cannot be counteracted, 
as can non-systematic errors, by increasing the least difference con- 
sidered significant, nor can the extent of error of this sort be measured 
or estimated by a study of the experimental results. 

Systematic error must therefore be reduced by every practicable 
means. Growing conditions in the preHminary test should be made as 
similar to ordinary field conditions as possible. The effect of varietal 
competition must be reduced to the minimum. If this can be ac- 
complished without increasing the size of plots, it is desirable to do 
so. On the other hand, if larger plots are necessary for the control 
of competition, larger plots should be used. If the area to be used 
for preliminary testing cannot be correspondingly increased, the num- 
ber of replications can be reduced sufficiently to permit the use of 
the larger plots required on the area available. This will necessitate 
a decrease in the degree of precision of the test, and will reduce the 
rapidity of elimination of the less valuable varieties. But is it not 
better to eliminate the undesirable varieties slowly than to risk the 
elimination of desirable ones by a more rapid analysis? 



74 Missouri Agr. Exp. Sta. Research Bulletin 49 

The error from competition is greater when different varieties 
are compared than when different strains of the same variety are 
compared, and the extent of error is roughly in proportion to the de- 
gree of difference in type of the varieties tested. Competition was 
not found to be correlated closely enough with earliness of heading, 
earliness of maturity, height, or grain-straw ratio in these experi- 
ments to permit its control by grouping varieties in respect to these 
characters. The factor found most closely correlated with competitive 
value was yield, but the correlation even in this case was not close 
enough to permit of effective control by grouping varieties. Moreover, 
it would be impossible in practice to group varieties with regard to 
yield, since the relative yield of varieties varies so widely with the 
season. The variety expected to yield poorly is not ordinarily included 
in the variety test. 

When different strains of the same variety are grown, the error 
from competition, in some cases at least, may be slight enough to 
justify the use of single-row plots. However, competition in such 
cases is not wholly absent, and may occasionally be quite marked. The 
importance of competition as a source of error in tests of pure line 
selections of the same variety merits detailed investigation. If it is 
found that the effects of competition between pure lines is slight it 
may be practicable to use single-row plots, or at any rate to use 3-row 
plots without discarding border rows. The latter method will reduce 
the error from competition materially, without necessitating the loss 
of any of the experimental area. When the same total area is used, 
however, single row plots are somewhat more reliable than 3-row 
plots, because more replications can be used. The best size of plot for 
ordinary variety testing, as indicated by this investigation, is probably 
the 3-row plot with border rows discarded. The length of the plot 
as harvested is assumed to be 16 feet, but the same considerations will 
apply for any other convenient length. The number of replications 
will vary with the heterogeneity of the field and the degree of precision 
required (and, to some extent, with the season and the variety), 

Check plots have been used in preliminary variety tests mainly 
for the following purposes : 

(1) For the adjustment of the yields of the test plots, and 

(2) To provide a measure of plot variability for the field used, 
and thus to determine the degree of precision of the experimental re- 
sults, or the number of replications which would be required for a 
given degree of precision. 

In both cases the behavior of the check variety is the basis for 
conclusions regarding the tested varieties. This involves the as- 
sumption that different varieties of the same crop respond similarly 



Experiments in Field Plot Technic 75 

to varying conditions. In one case, reported in this paper, two stand- 
ard varieties, used as duplicate checks, and grown side by side in 
120 distributed sections of a field, showed no significant correlation 
in relative yield of adjoining plots, and differed so widely in plot varia- 
bility that the number of replications necessary for a given degree of 
accuracy was more than twice as great for one check variety as for the 
other. Further investigation is necessary to determine how generally 
such cases may occur, but this single case indicates at least a possible 
source of extreme error in the use of check plots, either for adjust- 
ment of yield or for the determination of the probable error of the 
experimental results. 

For this and various other reasons the adjustment of yields by 
means of check plots is at present of doubtful value as a general prac- 
tice. In some cases, however, such adjustment accomplishes a great 
improvement in the precision of an experiment, with a relatively slight 
increase in expense. The practice is more promising for tests of 
strains or selections of the same variety than for tests of different 
types. A thorough study of the use of check plots in variety and strain 
testing may discover methods of overcoming the disadvantages, and 
thus make available an economical and effective method of increasing 
precision. Meanwhile, check plots should be used cautiously. Meth- 
ods for adjusting yields and for determining the extent of plot varia- 
bility without the use of check plots are available"' '', and check 
plots must demonstrate actual value if they are to continue in use in 
variety tests. 

SUMMARY 

1. In variety and strain tests of barley, oats, and wheat, in five- 
row blocks, the competing border rows of adjacent sorts gave relative 
yields often widely different from those of the interior rows of the 
same plots. 

2. Such competitive effects were much more extreme between 
different varieties than between different commercial strains of the 
same variety. 

3. A considerable error from competition affected tests in rows 
running north and south, as well as those in rows running east and 
west. 

4. Although in general the higher yielding varieties were favored 
in competition, the reverse frequently occurred. In some cases a ma- 
terial advantage in yield in the interior rows was converted to a 
material disadvantage in yield in the border rows. 



76 Missouri Agr. Exp. Sta. Research Bulletin 49 

5. Competing quality was correlated fairly consistently with 
yield and with earliness of heading and maturity. No relation to 
grain-straw ratio was found in the one season in which this charac- 
ter was determined. A significant correlation between competition 
and height was found in the wheat variety test of 1921, but the rela- 
tion of competition to height was not determined in the other tests. 

6. In the oats tests competition was most closely related to earli- 
ness of heading and maturity, but was also related to yield. In the 
wheat, competition was related fairly closely to both yield and earliness. 
In the barley it was not significantly correlated with any of the char- 
acteristics studied, though the relation to yield was considerably closer 
than the relation to any of the other characteristics. 

7. In the wheat and oats tests in which earliness and yield were 
correlated with competition, earliness and yield were correlated quite 
closely with one another. 

8. Single-row plots, protected from competition by border rows 
discarded at harvesting, were somewhat more variable in yield than 
3-row plots similarly protected, but the difference was not great 
enough to outweigh their advantage in size. The mean yield of five 
replicate protected single-row plots is therefore more reliable, under 
the conditions of these tests, than the mean yield of three replicate 
protected 3-row plots, which would occupy the same area and require 
considerably more labor in harvesting and threshing. 

9. There was no consistent difference in variability between 3- 
row and 5-row plots. 

10. Plot variability was increased with increase in the size of the 
experiment field. The number of replications required for a given 
degree of precision, as measured by the variability of plot yields, is 
therefore increased somewhat when border rows are added for the 
control of competition. 

11. The variability of 120 distributed check plots of Kherson oats 
dififered widely from that of 120 distributed plots of Red Rustproof 
oats, adjacent to them. If the variability of the check yields were con- 
sidered a measure of the precision of the test, entirely different con- 
clusions would be drawn on the basis of the yields of these two check 
varieties. 

12. Adjustment of plot yields on the basis of the yields of check 
plots resulted in a decrease in plot variability in three tests and in an 
increase in five tests. In general the practice was effective on fields of 
high plot variability, and was ineffective on fields of low plot varia- 
bility. 



Expe;riments in Field Plot Technic 77 

13. In the oats strain test in which both Kherson and Red Rust- 
proof check plots were included, the Kherson check was more effect- 
ive than the Red Rustproof check as a basis for adjusting the yields of 
the Kherson strains, while the Red Rustproof check was more ef- 
fective as a basis for adjusting the yields of the Red Rustproof strains. 

14. The correlation between the yields of adjacent Kherson and 
Red Rustproof check plots was not statistically significant. Adjust- 
ment of the yields of the Kherson check plots on the basis of the 
yields of the adjacent Red Rustproof plots, and of those of the 
Red Rustproof plots on the basis of the Kherson yields increased va- 
riability. 



ACKNOWLEDGMENT 

The writer is indebted to Professors M. F. Miller and W. C. 
Etheridge for a critical reading of the manuscript, and to O. W. 
Letson for preparing figure 8. 



78 Missouri Agr. Exp. Sta. Research Bulletin 49 



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of plats to probable error in field experimentation. In Journ. Amer. Soc. 
Agron. 12, 3 ; pp. 100-105. 1920. 

2. Etheridge, W. C. A classification of the varieties of cultivated oats. Cor- 

nell Univ. Agr. Expt. Sta. Memoir 10; pp. 85-172. 1916. 

3. Hall, A. D. and E. J. Russell. Field trials and their interpretation. In 

Jour. Bd. Agr. (London) Supplement: pp. 5-14. 1911. 

4. Hayes, H. K. and A. C. Arny. Experiments in field technic in rod-row 

tests. In Jour. Agr. Res., 11, 9: pp. 399-419. 1917. 

5. Kiesselbach, T. A. Studies concerning the elimination of experimental error 

in comparative crop tests. Nebr. Agr. Expt. Sta. Res. Bui. 13: pp. 3-95. 
1918. 

6. Kiesselbach, T. A. Experimental error in field trials. In Journ. Amer. Soc. 

Agron. 11, 6: pp. 235-241. 1919. 

7. Kiesselbach, T. A. Plat competition as a source of error in crop tests. In 

Journ. Amer. Soc. Agron. 11, 6: pp. 242-247. 1919. 

8. Love, H. H. The experimental error in field trials. In Journ. Amer. Soc. 

Agron. 11, 5: pp. 212-216. 1919. 

9. Love, H. H. and W. T. Craig. Methods used and results obtained in cereal 

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BIOGRAPHICAL NOTE 

Lewis John Stadler, born in St. Louis, Missouri, July 6, 1896, 
attended the University of Missouri during the years 1913-1915, and 
the University of Florida during the year 1916-1917; and was gradu- 
ated from the latter-named institution in 1917 with the degree of 
Bachelor of Science in Agriculture. He pursued graduate studies 
in field crops, botany, plant breedin'g, and soils at the University of 
Missouri and for a term at Cornell University, during the years 1917- 
1922, holding a fellowship in cereal crop improvement at the Univer- 
sity of Missouri in the scholastic year 1917-1918, and receivin'g the 
degree of Master of Arts in 1918. Since May 1920 he has been x\s- 
sistant Professor of Field Crops at the University of Missouri. 



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